{"id":56802,"date":"2026-09-11T08:27:15","date_gmt":"2026-09-11T08:27:15","guid":{"rendered":"https:\/\/zobai.com\/?p=56802"},"modified":"2026-09-24T12:19:29","modified_gmt":"2026-09-24T12:19:29","slug":"how-to-calculate-built-up-back-pressure-in-safety-valve-discharge-piping","status":"publish","type":"post","link":"https:\/\/zobai.com\/ru\/blog\/how-to-calculate-built-up-back-pressure-in-safety-valve-discharge-piping\/","title":{"rendered":"\u041a\u0430\u043a \u0440\u0430\u0441\u0441\u0447\u0438\u0442\u0430\u0442\u044c \u043d\u0430\u043a\u043e\u043f\u043b\u0435\u043d\u043d\u043e\u0435 \u043f\u0440\u043e\u0442\u0438\u0432\u043e\u0434\u0430\u0432\u043b\u0435\u043d\u0438\u0435 \u0432 \u0441\u0431\u0440\u043e\u0441\u043d\u043e\u043c \u0442\u0440\u0443\u0431\u043e\u043f\u0440\u043e\u0432\u043e\u0434\u0435 \u043f\u0440\u0435\u0434\u043e\u0445\u0440\u0430\u043d\u0438\u0442\u0435\u043b\u044c\u043d\u043e\u0433\u043e \u043a\u043b\u0430\u043f\u0430\u043d\u0430"},"content":{"rendered":"<style> .zobai-builtup-bp-guide { max-width: 100%; } .zobai-builtup-bp-guide .zobai-table-wrap { width: 100%; overflow-x: auto; -webkit-overflow-scrolling: touch; margin: 1.25rem 0; } .zobai-builtup-bp-guide table { width: 100%; min-width: 640px; border-collapse: collapse; } .zobai-builtup-bp-guide th, .zobai-builtup-bp-guide td { padding: 0.75rem; vertical-align: top; border: 1px solid rgba(0, 0, 0, 0.14); text-align: left; } .zobai-builtup-bp-guide .zobai-equation { max-width: 100%; overflow-x: auto; -webkit-overflow-scrolling: touch; white-space: nowrap; padding: 0.8rem 0; margin: 1rem 0; } .zobai-builtup-bp-guide .zobai-equation code { font-size: 1em; white-space: nowrap; } .zobai-builtup-bp-guide .zobai-note { margin: 1.25rem 0; padding: 1rem 1.1rem; border-left: 3px solid currentColor; } .zobai-builtup-bp-guide .zobai-decision-path { margin: 1.25rem 0; padding: 1rem 1.1rem; border: 1px solid rgba(0, 0, 0, 0.14); } .zobai-builtup-bp-guide .zobai-cta { margin-top: 2rem; padding: 1.25rem; border: 1px solid rgba(0, 0, 0, 0.14); } .zobai-builtup-bp-guide a { overflow-wrap: anywhere; } @media (max-width: 767px) { .zobai-builtup-bp-guide table { min-width: 600px; } .zobai-builtup-bp-guide .zobai-note, .zobai-builtup-bp-guide .zobai-decision-path, .zobai-builtup-bp-guide .zobai-cta { padding: 0.9rem; } } <\/style>\n<article class=\"zobai-builtup-bp-guide\">\n<p><strong>Built-up back pressure is the portion of pressure at a safety-valve outlet created by relieving flow through the downstream discharge path.<\/strong> It is different from <strong>superimposed back pressure<\/strong>, which is already present at the outlet before the subject valve opens because of pressure from the downstream system or other sources. During relieving, the valve can see the combined effect of both components.<\/p>\n<p>That distinction is not just terminology. It controls the calculation boundary. For a tailpipe discharging to atmosphere, the downstream pressure may be close to atmospheric and most outlet pressure during flow is generated by the branch itself. For a valve discharging into a closed or common header, part of the outlet pressure may already exist before the valve opens, and additional pressure is then generated by the subject relief flow and possibly by interacting relief streams elsewhere in the network.<\/p>\n<p>A reliable built-up back-pressure calculation therefore has five steps: <strong>define the pressure component and boundary \u2192 establish the correct outlet-flow basis \u2192 choose a hydraulic method appropriate to the fluid state \u2192 solve the installed discharge path \u2192 compare the resulting outlet condition with the exact valve\/configuration and project basis.<\/strong><\/p>\n<p>Calculating back pressure and deciding whether a safety valve can tolerate that back pressure are separate engineering tasks. LESER&#8217;s engineering manual defines total back pressure as the sum of built-up and superimposed back pressure and notes that back pressure can influence safety-valve function. Emerson&#8217;s pressure-relief-valve handbook likewise treats built-up and superimposed back pressure as distinct inputs and shows that the effect on set pressure, lift, reseating and capacity depends on valve architecture and service. <a href=\"https:\/\/www.leser.com\/-\/media\/files\/engineering\/leser_engineering.pdf\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">LESER Engineering manual<\/a>; <a href=\"https:\/\/www.emerson.com\/documents\/automation\/pressure-relief-valve-engineering-handbook-cs-cz-4262398.pdf\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">Emerson Pressure Relief Valve Engineering Handbook<\/a>.<\/p>\n<p>No universal back-pressure percentage is used in this guide. Allowable back pressure, any capacity correction, and stability limits must come from the governing standard\/project basis and the exact manufacturer documentation for the candidate valve.<\/p>\n<section>\n<h2>What Built-Up Back Pressure Are You Actually Calculating?<\/h2>\n<p>Before calculating pipe friction, identify which outlet-side pressure quantity you are dealing with and when that pressure exists.<\/p>\n<h3>Built-up, superimposed and total back pressure are different quantities<\/h3>\n<div class=\"zobai-table-wrap\" role=\"region\" aria-label=\"Comparison of safety valve back-pressure components\" tabindex=\"0\">\n<table>\n<thead>\n<tr>\n<th scope=\"col\">Pressure quantity<\/th>\n<th scope=\"col\">Engineering meaning<\/th>\n<th scope=\"col\">Typical question<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td><strong>Built-up back pressure<\/strong><\/td>\n<td>Pressure generated at the safety-valve outlet by relieving flow through the valve and downstream discharge system.<\/td>\n<td>How much outlet pressure does this relief flow create because of branch\/header resistance?<\/td>\n<\/tr>\n<tr>\n<td><strong>Superimposed back pressure<\/strong><\/td>\n<td>Pressure present at the valve outlet when the valve is called upon to operate, caused by other downstream-system sources.<\/td>\n<td>What pressure is already present before this valve contributes its own relieving flow?<\/td>\n<\/tr>\n<tr>\n<td><strong>Total back pressure during relieving<\/strong><\/td>\n<td>The outlet pressure seen by the valve during the event, resulting from the applicable superimposed and built-up components.<\/td>\n<td>What outlet-pressure condition must the valve actually operate against?<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>LESER&#8217;s engineering manual uses the relationship <strong>Back Pressure = Built-up + Superimposed<\/strong> as the conceptual starting point. It also distinguishes an open-air outlet line, where relieving flow generates built-up back pressure, from a closed blowdown\/discharge system where superimposed pressure can exist before the subject valve opens. <a href=\"https:\/\/www.leser.com\/-\/media\/files\/engineering\/leser_engineering.pdf\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">LESER, Installation and Plant Design<\/a>.<\/p>\n<p>This becomes especially important in a common header. A branch pressure-drop calculation can be correct yet incomplete if the engineer treats the header pressure as zero or atmospheric when another source has already pressurized the header.<\/p>\n<div class=\"zobai-note\">\n<p><strong>Illustrative engineering scenario:<\/strong> A safety valve that originally discharged through a dedicated tailpipe is later connected to a common relief header. Recalculating only the friction generated by the branch flow captures the built-up component but can miss pre-existing header pressure. The prevention step is to establish the credible superimposed header-pressure range first, then calculate the additional pressure generated by the subject relieving flow.<\/p>\n<\/div>\n<h3>Define the reference point before doing the hydraulics<\/h3>\n<p>In the ISO 4126-9-based outlet-line calculation route reproduced in the LESER manual:<\/p>\n<ul>\n<li><strong>P<sub>b<\/sub><\/strong> is the pressure at the safety-valve outlet during discharge;<\/li>\n<li><strong>P<sub>u<\/sub><\/strong> is the pressure at the downstream end of the calculated discharge path and, in the LESER formulation, represents the superimposed downstream pressure, often atmospheric;<\/li>\n<li><strong>P<sub>b<\/sub> \u2212 P<sub>u<\/sub><\/strong> is the pressure rise generated through the defined downstream path in that model.<\/li>\n<\/ul>\n<aside class=\"zobai-note\">\n<p><strong>Calculation rule:<\/strong> Define where P<sub>b<\/sub> is evaluated, what physical node P<sub>u<\/sub> represents, and whether P<sub>u<\/sub> is fixed or itself depends on other relief flows before calculating pipe resistance.<\/p>\n<\/aside>\n<p>Without that boundary definition, a pressure-drop result can be numerically correct while answering the wrong engineering question.<\/p>\n<\/section>\n<section>\n<h2>Define the Discharge-Piping Calculation Boundary and Required Inputs<\/h2>\n<p>A built-up back-pressure calculation needs a physical boundary. Trace the discharge path from the safety-valve outlet to a downstream point where pressure is known, can be conservatively bounded, or is determined by a system-level hydraulic calculation.<\/p>\n<p>The destination might be atmosphere, a closed receiver, a vent system, a flare\/relief header, or another containment system. What matters is <strong>the pressure at the end of the calculation, how that pressure is established, and whether it changes when other relief sources operate.<\/strong><\/p>\n<figure class=\"wp-block-image size-full zobai-figure\" data-image-slot=\"IMG-01\"><img loading=\"lazy\" src=\"https:\/\/zobai.com\/wp-content\/uploads\/2026\/09\/built-up-back-pressure-discharge-piping-img-01.webp\" alt=\"Safety valve discharge-piping calculation boundary showing valve outlet pressure, downstream piping resistance and terminal pressure.\" title=\"How to Calculate Built-Up Back Pressure in Safety Valve Discharge Piping - IMG-01\" width=\"1200\" height=\"900\" class=\"wp-image-56854\" loading=\"lazy\" decoding=\"async\" srcset=\"https:\/\/zobai.com\/wp-content\/uploads\/2026\/09\/built-up-back-pressure-discharge-piping-img-01.webp 1200w, https:\/\/zobai.com\/wp-content\/uploads\/2026\/09\/built-up-back-pressure-discharge-piping-img-01-300x225.webp 300w, https:\/\/zobai.com\/wp-content\/uploads\/2026\/09\/built-up-back-pressure-discharge-piping-img-01-1024x768.webp 1024w, https:\/\/zobai.com\/wp-content\/uploads\/2026\/09\/built-up-back-pressure-discharge-piping-img-01-768x576.webp 768w, https:\/\/zobai.com\/wp-content\/uploads\/2026\/09\/built-up-back-pressure-discharge-piping-img-01-16x12.webp 16w, https:\/\/zobai.com\/wp-content\/uploads\/2026\/09\/built-up-back-pressure-discharge-piping-img-01-400x300.webp 400w\" sizes=\"auto, (max-width: 1200px) 100vw, 1200px\" \/><figcaption>Safety valve discharge-piping calculation boundary showing valve outlet pressure, downstream piping resistance and terminal pressure.<\/figcaption><\/figure>\n<h3>Start with the defined relief case<\/h3>\n<p>The required process relief rate is not automatically the correct discharge-piping calculation flow for every pressure-relief device and operating characteristic.<\/p>\n<p>Emerson&#8217;s engineering handbook, summarizing API 521 practice, notes that outlet-line pressure-loss calculations may use <strong>rated capacity for some direct spring-operated PRVs<\/strong> while a <strong>required-capacity basis can be appropriate for modulating pilot-operated designs<\/strong>. The important decision is therefore not \u201calways use required flow\u201d or \u201calways use rated flow,\u201d but <strong>identify the flow basis required by the governing method and the actual valve operating behavior<\/strong>. <a href=\"https:\/\/www.emerson.com\/documents\/automation\/pressure-relief-valve-engineering-handbook-cs-cz-4262398.pdf\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">Emerson PRV Engineering Handbook<\/a>.<\/p>\n<aside class=\"zobai-note\">\n<p><strong>Ask this before calculating:<\/strong> What flow can this valve send into the discharge path for the applicable relief case and calculation basis?<\/p>\n<\/aside>\n<div class=\"zobai-note\">\n<p><strong>Illustrative engineering scenario:<\/strong> The process relief load is used directly as the outlet-pipe flow for a snap-acting spring valve, even though the selected downstream method\/manufacturer basis calls for a higher rated discharge flow. The calculated built-up back pressure can then be understated. The prevention step is to freeze the valve type and outlet-flow basis before solving the piping hydraulics.<\/p>\n<\/div>\n<p>If the required relief load itself has not yet been established, that is an upstream sizing task. See the <a href=\"\/blog\/safety-valve-sizing-and-certified-relieving-capacity-guide\/\">Safety Valve Sizing Guide<\/a>; this article treats the applicable outlet-flow basis as an input rather than recalculating the entire overpressure scenario.<\/p>\n<h3>Collect the fluid and relieving-condition inputs<\/h3>\n<p>The calculation package should identify, as applicable:<\/p>\n<ul>\n<li>whether the discharge is single-phase liquid, gas\/vapor, steam, or potentially two-phase;<\/li>\n<li>relieving pressure and temperature;<\/li>\n<li>fluid properties required by the selected hydraulic method;<\/li>\n<li>the required, rated, or otherwise applicable discharge-flow basis;<\/li>\n<li>safety-valve flow area and discharge-coefficient data when the selected method uses them;<\/li>\n<li>any downstream flashing, condensation, reaction, or composition change that could invalidate the assumed fluid model.<\/li>\n<\/ul>\n<p>Use properties that correspond to the relieving conditions and the selected method rather than substituting unrelated normal-operating data simply because those values are already available on a process datasheet.<\/p>\n<h3>Map the actual discharge path<\/h3>\n<p>Record the hydraulic path rather than only the nominal outlet size:<\/p>\n<ul>\n<li>actual pipe internal diameters and schedule\/roughness inputs where required;<\/li>\n<li>straight lengths;<\/li>\n<li>elbows and fittings;<\/li>\n<li>valves or restrictions;<\/li>\n<li>reducers and expanders;<\/li>\n<li>silencers, flame arresters, rupture discs, separators, or other downstream equipment if present;<\/li>\n<li>elevation changes where the method requires them;<\/li>\n<li>branch and header geometry for common disposal systems.<\/li>\n<\/ul>\n<p>A calculation based only on straight-pipe length will not represent an installed path containing significant local resistance. Mechanical installation questions outside this hydraulic task belong in the <a href=\"\/engineering\/safety-valve-installation-guide\/\">Safety Valve Installation Guide<\/a>.<\/p>\n<h3>Define the downstream pressure boundary<\/h3>\n<p>Finally, define P<sub>u<\/sub>, or the equivalent downstream pressure used by the selected method.<\/p>\n<p>For an atmospheric discharge, the terminal condition differs from a valve connected to a pressurized closed header. In a shared header, the boundary may depend on other relieving sources, flare-system hydraulics, purge\/blanketing conditions, receiver pressure, or the specific simultaneous-relief case under review.<\/p>\n<div class=\"zobai-table-wrap\" role=\"region\" aria-label=\"Required built-up back-pressure calculation inputs\" tabindex=\"0\">\n<table>\n<thead>\n<tr>\n<th scope=\"col\">Input group<\/th>\n<th scope=\"col\">What to establish<\/th>\n<th scope=\"col\">Why it changes the calculation<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Relief case<\/td>\n<td>Applicable discharge-flow basis for the selected valve\/method<\/td>\n<td>Defines the load entering the outlet system.<\/td>\n<\/tr>\n<tr>\n<td>Fluid state<\/td>\n<td>Single-phase liquid, gas\/vapor, steam, or potentially two-phase<\/td>\n<td>Determines the hydraulic model.<\/td>\n<\/tr>\n<tr>\n<td>Relieving conditions<\/td>\n<td>Pressure, temperature and required properties<\/td>\n<td>Defines density, compressibility and other flow inputs.<\/td>\n<\/tr>\n<tr>\n<td>Valve data<\/td>\n<td>Flow area, discharge coefficient and rated\/required flow basis where needed<\/td>\n<td>Connects device behavior to the downstream calculation.<\/td>\n<\/tr>\n<tr>\n<td>Pipe geometry<\/td>\n<td>Actual internal diameter, length and relevant roughness basis<\/td>\n<td>Controls flow area and distributed resistance.<\/td>\n<\/tr>\n<tr>\n<td>Components<\/td>\n<td>Fittings, valves, reducers, expanders and downstream equipment<\/td>\n<td>Adds local resistance or changes fluid behavior.<\/td>\n<\/tr>\n<tr>\n<td>Elevation<\/td>\n<td>Relevant vertical changes<\/td>\n<td>May contribute to the pressure balance, especially for liquid service.<\/td>\n<\/tr>\n<tr>\n<td>Terminal condition<\/td>\n<td>Pressure at atmosphere, receiver, header or other downstream node<\/td>\n<td>Establishes the hydraulic boundary.<\/td>\n<\/tr>\n<tr>\n<td>Shared-system state<\/td>\n<td>Other simultaneous relief flows or variable header pressure<\/td>\n<td>Can make the downstream boundary case-dependent rather than fixed.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>Before proceeding, the calculation basis should answer four questions: <strong>What flow is being discharged? What fluid state\/model is being used? What physical path is included? What pressure exists at the end of that path for the credible case?<\/strong><\/p>\n<\/section>\n<section>\n<h2>How to Calculate Built-Up Back Pressure for a Liquid Relief Case<\/h2>\n<p>For a defined <strong>single-phase liquid<\/strong> case, LESER&#8217;s Engineering manual reproduces the ISO 4126-9 outlet-line relation between discharge-system resistance and pressure at the valve outlet. It is a standards-based method for a defined calculation model, not a universal formula for every liquid relief system. <a href=\"https:\/\/www.leser.com\/-\/media\/files\/engineering\/leser_engineering.pdf\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">LESER Engineering manual, Installation and Plant Design<\/a>.<\/p>\n<div class=\"zobai-equation\" role=\"math\" aria-label=\"Pb minus Pu divided by P0 minus Pb equals zeta A multiplied by the square of Kdr A divided by 0.9 AA\">\n  <code>(P<sub>b<\/sub> \u2212 P<sub>u<\/sub>) \/ (P<sub>0<\/sub> \u2212 P<sub>b<\/sub>) = \u03b6<sub>A<\/sub> [K<sub>dr<\/sub>A \/ (0.9A<sub>A<\/sub>)]<sup>2<\/sup><\/code>\n<\/div>\n<p><strong>For this displayed relation, P<sub>0<\/sub>, P<sub>b<\/sub> and P<sub>u<\/sub> are absolute pressures and must use one consistent pressure basis.<\/strong> LESER identifies P<sub>u<\/sub> as the pressure at the pipe end (superimposed back pressure, often atmospheric), while P<sub>b<\/sub> is the back pressure at the valve outlet during discharge. The difference P<sub>b<\/sub> \u2212 P<sub>u<\/sub> is therefore the built-up pressure generated across the defined outlet path in this model.<\/p>\n<p>where:<\/p>\n<ul>\n<li><strong>P<sub>0<\/sub><\/strong> = relieving pressure, absolute;<\/li>\n<li><strong>P<sub>b<\/sub><\/strong> = pressure\/back pressure at the valve outlet during discharge, absolute;<\/li>\n<li><strong>P<sub>u<\/sub><\/strong> = pressure at the end of the calculated discharge path, absolute;<\/li>\n<li><strong>A<\/strong> = safety-valve flow area;<\/li>\n<li><strong>A<sub>A<\/sub><\/strong> = flow area of the outlet pipe;<\/li>\n<li><strong>K<sub>dr<\/sub><\/strong> = certified derated coefficient of discharge used by the method;<\/li>\n<li><strong>\u03b6<sub>A<\/sub><\/strong> = pressure-loss coefficient of the discharge pipe including elbows, silencer or other fittings represented by the method.<\/li>\n<\/ul>\n<p>The value of the relation is not that it creates a one-line shortcut. It forces the calculation to link valve flow geometry, outlet-pipe geometry, downstream resistance, relieving pressure and the defined downstream pressure boundary.<\/p>\n<h3>Establish the liquid-flow calculation basis<\/h3>\n<p>First confirm that the service can legitimately be treated as <strong>single-phase liquid<\/strong> for the selected method.<\/p>\n<p>ISO 4126-10:2024 is the current published ISO standard specifically addressing gas\/liquid two-phase sizing. It also notes that pressure calculations within that document use absolute pressure. If significant flashing or two-phase flow is credible in the safety device or connected outlet system, do not force the problem through the single-phase liquid relation merely by choosing a different density. <a href=\"https:\/\/www.iso.org\/standard\/76057.html\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">ISO 4126-10:2024<\/a>.<\/p>\n<h3>Calculate straight-pipe and local resistance<\/h3>\n<p>The discharge resistance represented by \u03b6<sub>A<\/sub> can include distributed pipe resistance and local component losses.<\/p>\n<div class=\"zobai-equation\" role=\"math\" aria-label=\"Conceptual total resistance equals lambda L divided by D plus the sum of local zeta coefficients\">\n  <code>\u03b6<sub>A<\/sub> = \u03bbL\/D + \u03a3\u03b6<sub>i<\/sub><\/code>\n<\/div>\n<p>when that representation is consistent with the selected hydraulic method.<\/p>\n<ul>\n<li><strong>\u03bbL\/D<\/strong> represents straight-pipe resistance;<\/li>\n<li><strong>\u03a3\u03b6<sub>i<\/sub><\/strong> represents local resistance from fittings and components.<\/li>\n<\/ul>\n<p>Use one internally consistent resistance representation. If an elbow is already converted into equivalent pipe length, adding the same full local-loss coefficient again would double-count that resistance.<\/p>\n<h3>Include static-head effects where applicable<\/h3>\n<p>Elevation is a pressure-balance contribution rather than friction. It can matter materially in liquid discharge piping, but the way it is included depends on the selected calculation method.<\/p>\n<p>Do not splice a standalone \u03c1g\u0394z term into a standards equation unless the chosen method and pressure definitions support that treatment. The safer workflow is to keep friction, local losses, elevation and downstream pressure within one documented hydraulic model.<\/p>\n<h3>Build the pressure-loss calculation from outlet to boundary<\/h3>\n<p>For calculation convenience, define:<\/p>\n<div class=\"zobai-equation\" role=\"math\" aria-label=\"R equals zeta A multiplied by the square of Kdr A divided by 0.9 AA\">\n  <code>R = \u03b6<sub>A<\/sub> [K<sub>dr<\/sub>A \/ (0.9A<sub>A<\/sub>)]<sup>2<\/sup><\/code>\n<\/div>\n<p>The same relation can then be rearranged algebraically:<\/p>\n<div class=\"zobai-equation\" role=\"math\" aria-label=\"Pb equals Pu plus R P0 divided by one plus R\">\n  <code>P<sub>b<\/sub> = (P<sub>u<\/sub> + RP<sub>0<\/sub>) \/ (1 + R)<\/code>\n<\/div>\n<p>and the built-up component over the defined downstream boundary is:<\/p>\n<div class=\"zobai-equation\" role=\"math\" aria-label=\"Built-up pressure difference equals Pb minus Pu\">\n  <code>\u0394P<sub>built-up<\/sub> = P<sub>b<\/sub> \u2212 P<sub>u<\/sub><\/code>\n<\/div>\n<p>P<sub>u<\/sub> remains the downstream\/superimposed boundary in this LESER\/ISO calculation route; P<sub>b<\/sub> \u2212 P<sub>u<\/sub> is the generated built-up component.<\/p>\n<h3>Worked single-phase liquid calculation structure<\/h3>\n<ol>\n<li>Confirm that a single-phase liquid method is valid for the case.<\/li>\n<li>Record absolute P<sub>0<\/sub> and P<sub>u<\/sub> on a consistent pressure basis.<\/li>\n<li>Record valve flow area A and actual discharge-pipe area A<sub>A<\/sub>.<\/li>\n<li>Establish the applicable K<sub>dr<\/sub> and its source.<\/li>\n<li>Calculate the complete downstream resistance coefficient \u03b6<sub>A<\/sub> without double counting fittings.<\/li>\n<li>Calculate R and solve for absolute P<sub>b<\/sub>.<\/li>\n<li>Calculate P<sub>b<\/sub> \u2212 P<sub>u<\/sub> as the built-up component for the defined path.<\/li>\n<li>Carry P<sub>b<\/sub>, the superimposed range, and the built-up component into the valve-specific acceptance review.<\/li>\n<\/ol>\n<aside class=\"zobai-note\">\n<p><strong>Scope:<\/strong> This is a single-phase liquid calculation structure tied to the cited LESER\/ISO 4126-9 route. It is not a flashing\/two-phase method and it is not automatically the governing method for every jurisdiction or project.<\/p>\n<\/aside>\n<\/section>\n<section>\n<h2>How to Calculate Built-Up Back Pressure for Gas or Vapor Relief<\/h2>\n<p>Gas and vapor discharge need a compressible-flow treatment because density, velocity and pressure are coupled through the downstream system.<\/p>\n<p>A constant-density liquid pressure-drop model is therefore not automatically valid for a safety-valve gas or vapor discharge.<\/p>\n<h3>Why gas or vapor cannot be treated like an incompressible liquid<\/h3>\n<p>As gas pressure falls through the outlet system, density and velocity change together. Pressure ratios, temperature and thermodynamic properties can become important, and critical-flow conditions can occur at more than one location in the overall relief path.<\/p>\n<p>The need for a separate method comes from this coupling between pressure, density and velocity\u2014not simply from the fact that a gas is \u201clighter\u201d than a liquid.<\/p>\n<h3>Account for changing pressure, density and flow conditions<\/h3>\n<p>Depending on the selected compressible-flow method, relevant inputs can include:<\/p>\n<ul>\n<li>relieving pressure and downstream\/superimposed pressure;<\/li>\n<li>relieving temperature;<\/li>\n<li>ratio of specific heats or other thermodynamic properties required by the method;<\/li>\n<li>compressibility\/real-gas data where applicable;<\/li>\n<li>outlet-flow basis for the selected valve behavior;<\/li>\n<li>safety-valve flow area;<\/li>\n<li>outlet-pipe flow area;<\/li>\n<li>applicable discharge coefficient;<\/li>\n<li>total piping resistance and geometry.<\/li>\n<\/ul>\n<p>The properties and pressure basis should come from one documented compressible-flow method rather than from a mixture of unrelated gas-flow equations.<\/p>\n<h3>Check whether critical or choked-flow behavior changes the method<\/h3>\n<p>LESER&#8217;s Engineering manual, applying the ISO 4126-9 outlet-line method, includes a check for a possible second critical-flow condition at the outlet-pipe end:<\/p>\n<div class=\"zobai-equation\" role=\"math\" aria-label=\"Pc divided by P0 equals the critical pressure ratio term multiplied by Kdr A divided by 0.9 AA\">\n  <code>P<sub>c<\/sub>\/P<sub>0<\/sub> = [2\/(k + 1)]<sup>k\/(k \u2212 1)<\/sup> \u00d7 K<sub>dr<\/sub>A\/(0.9A<sub>A<\/sub>)<\/code>\n<\/div>\n<p><strong>This relationship checks the potential critical condition at the pipe outlet; it does not by itself calculate the complete valve-outlet pressure P<sub>b<\/sub>.<\/strong> Use the pressure basis required by the selected method consistently, including absolute pressure where specified.<\/p>\n<aside class=\"zobai-note\">\n<p><strong>Engineering implication:<\/strong> Critical flow is not necessarily confined to the safety-valve nozzle. A downstream restriction or pipe-end condition can become another limiting location in a compressible discharge path.<\/p>\n<\/aside>\n<h3>Solve the discharge path to the defined downstream condition<\/h3>\n<ol>\n<li>Establish the applicable outlet-flow basis for the valve and relief case.<\/li>\n<li>Define relieving and downstream pressures on the basis required by the selected method.<\/li>\n<li>Obtain the thermodynamic properties required by that method.<\/li>\n<li>Calculate resistance through the actual outlet path.<\/li>\n<li>Evaluate any critical\/choked condition required by the method.<\/li>\n<li>Solve the compressible-flow relationship for the branch\/header boundary being analyzed.<\/li>\n<li>Recalculate after material piping or boundary-condition changes.<\/li>\n<\/ol>\n<p>For a complicated compressible network, a validated hydraulic model can be more appropriate than a compact hand equation. Software does not remove the need to define the relief case, outlet-flow basis, fluid model and downstream boundary correctly.<\/p>\n<\/section>\n<section>\n<h2>How Fittings, Elevation and a Closed or Common Header Affect the Calculation<\/h2>\n<p>A real safety-valve discharge system rarely consists of one constant-diameter straight pipe to atmosphere. The model needs to represent the actual hydraulic path while keeping superimposed and built-up pressure conceptually separate.<\/p>\n<figure class=\"wp-block-image size-full zobai-figure\" data-image-slot=\"IMG-02\"><img loading=\"lazy\" src=\"https:\/\/zobai.com\/wp-content\/uploads\/2026\/09\/built-up-back-pressure-discharge-piping-img-02.webp\" alt=\"Common relief header showing superimposed downstream pressure and the built-up pressure contribution from one safety valve discharge branch.\" title=\"How to Calculate Built-Up Back Pressure in Safety Valve Discharge Piping - IMG-02\" width=\"1200\" height=\"900\" class=\"wp-image-56855\" loading=\"lazy\" decoding=\"async\" srcset=\"https:\/\/zobai.com\/wp-content\/uploads\/2026\/09\/built-up-back-pressure-discharge-piping-img-02.webp 1200w, https:\/\/zobai.com\/wp-content\/uploads\/2026\/09\/built-up-back-pressure-discharge-piping-img-02-300x225.webp 300w, https:\/\/zobai.com\/wp-content\/uploads\/2026\/09\/built-up-back-pressure-discharge-piping-img-02-1024x768.webp 1024w, https:\/\/zobai.com\/wp-content\/uploads\/2026\/09\/built-up-back-pressure-discharge-piping-img-02-768x576.webp 768w, https:\/\/zobai.com\/wp-content\/uploads\/2026\/09\/built-up-back-pressure-discharge-piping-img-02-16x12.webp 16w, https:\/\/zobai.com\/wp-content\/uploads\/2026\/09\/built-up-back-pressure-discharge-piping-img-02-400x300.webp 400w\" sizes=\"auto, (max-width: 1200px) 100vw, 1200px\" \/><figcaption>Common relief header showing superimposed downstream pressure and the built-up pressure contribution from one safety valve discharge branch.<\/figcaption><\/figure>\n<div class=\"zobai-table-wrap\" role=\"region\" aria-label=\"Treatment of discharge-system features in built-up back-pressure calculations\" tabindex=\"0\">\n<table>\n<thead>\n<tr>\n<th scope=\"col\">Discharge-system feature<\/th>\n<th scope=\"col\">How it affects the calculation<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Straight pipe<\/td>\n<td>Adds distributed resistance.<\/td>\n<\/tr>\n<tr>\n<td>Elbows, valves and fittings<\/td>\n<td>Add local resistance and can materially increase built-up pressure.<\/td>\n<\/tr>\n<tr>\n<td>Reducers and expanders<\/td>\n<td>Change area, velocity and local hydraulic behavior.<\/td>\n<\/tr>\n<tr>\n<td>Elevation<\/td>\n<td>Can modify the pressure balance according to fluid and calculation method.<\/td>\n<\/tr>\n<tr>\n<td>Pressurized receiver\/header<\/td>\n<td>Sets or influences the superimposed downstream pressure boundary.<\/td>\n<\/tr>\n<tr>\n<td>Other relief devices<\/td>\n<td>Can alter the shared-header pressure and therefore the pressure seen at the branch connection.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<h3>Include elbows, valves and diameter changes without double counting<\/h3>\n<p>Choose one consistent way of representing local resistance.<\/p>\n<p>If a fitting is represented using a local loss coefficient, include that coefficient once. If the selected method converts the fitting into equivalent pipe length, adding the same full local-loss contribution again would overstate resistance and therefore overstate built-up back pressure.<\/p>\n<h3>Treat elevation according to the applicable fluid calculation<\/h3>\n<p>Elevation is a pressure-balance contribution rather than friction.<\/p>\n<p>For liquid systems, hydrostatic head can materially affect the pressure balance. For gas\/vapor systems, the appropriate treatment depends on the selected compressible-flow model and properties.<\/p>\n<p>The elevation contribution should therefore follow the selected hydraulic method rather than being appended from an incompatible formula.<\/p>\n<h3>Separate downstream\/header pressure from the pressure generated by this discharge<\/h3>\n<div class=\"zobai-decision-path\">\n<p><strong>Before the subject valve opens:<\/strong><br \/>\n  existing downstream\/header pressure \u2192 superimposed back pressure<\/p>\n<p><strong>After the subject valve begins relieving:<\/strong><br \/>\n  pressure generated by its flow through branch\/header resistance \u2192 built-up contribution<\/p>\n<p><strong>At the valve outlet during relieving:<\/strong><br \/>\n  applicable superimposed component + built-up component \u2192 total back pressure seen by the valve<\/p>\n<\/div>\n<p>Emerson&#8217;s handbook notes that closed discharge systems can expose a PRV to both built-up and superimposed back pressure and that superimposed pressure may be constant or variable. It also describes the superimposed-pressure calculation as a system problem: determine which other devices can be operating and combine those effluent flows with the disposal-system geometry to determine pressure at the subject valve outlet. <a href=\"https:\/\/www.emerson.com\/documents\/automation\/pressure-relief-valve-engineering-handbook-cs-cz-4262398.pdf\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">Emerson PRV Engineering Handbook<\/a>.<\/p>\n<h3>Check whether other relief flows can change the system boundary<\/h3>\n<p>For the relevant relief scenario, ask:<\/p>\n<ul>\n<li>Can multiple devices relieve during the same credible event?<\/li>\n<li>Does their combined flow change the header pressure seen by this branch?<\/li>\n<li>Is superimposed back pressure constant, variable, or case-dependent?<\/li>\n<li>Can the branch still be represented by one defensible downstream boundary?<\/li>\n<li>Or does the problem require a coupled relief-header\/disposal-system model?<\/li>\n<\/ul>\n<div class=\"zobai-note\">\n<p><strong>Illustrative engineering scenario:<\/strong> A branch calculation assumes a fixed header pressure while another large PRV can discharge simultaneously in the governing plant event. The subject branch&#8217;s built-up friction may be calculated correctly, yet the total back pressure at the valve outlet is understated because the shared header pressure rises. The prevention step is to define simultaneous-relief cases and solve the interacting header hydraulics when they materially affect the branch boundary.<\/p>\n<\/div>\n<p>Once the downstream pressure depends materially on an interacting relief network, a single isolated tailpipe calculation may no longer represent the installed system. The broader relief\/disposal-system task belongs in ZOBAI&#8217;s <a href=\"\/standards\/api-521-pressure-relief-systems\/\">API 521 Pressure Relief Systems Guide<\/a>. API describes Standard 521 as guidance for pressure-relieving and depressuring systems in LNG terminals, petrochemical facilities, gas plants and other petroleum-production facilities; its scope should not be generalized to every industry. <a href=\"https:\/\/www.api.org\/products-and-services\/standards\/important-standards-announcements\/standard521\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">API Standard 521 scope<\/a>.<\/p>\n<\/section>\n<section>\n<h2>How to Interpret the Calculated Back Pressure<\/h2>\n<p><strong>A calculated built-up back pressure is a hydraulic result. It is not, by itself, an allowable valve limit or proof that a particular safety valve is suitable.<\/strong><\/p>\n<h3>Calculated built-up back pressure is not an allowable limit<\/h3>\n<p>The hydraulic calculation answers:<\/p>\n<p><strong>What outlet-side pressure is generated by the defined discharge path under the stated relieving-flow and boundary assumptions?<\/strong><\/p>\n<p>The valve\/application review answers a different question:<\/p>\n<p><strong>Can this exact valve configuration maintain the required set-pressure behavior, lift, stability, reseating behavior and applicable relieving capacity under the total outlet-pressure condition?<\/strong><\/p>\n<p>Those are different evidence sets. LESER notes that excessive built-up back pressure can contribute to chattering, while Emerson lists possible consequences of back pressure that include changes in set pressure, reseating pressure, lift stability and actual relieving capacity. Neither source supports replacing valve-specific data with one generic percentage for all safety valves. <a href=\"https:\/\/www.leser.com\/en\/leser-update\/10-2022\/function-chatter\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">LESER back-pressure\/chattering discussion<\/a>; <a href=\"https:\/\/www.emerson.com\/documents\/automation\/pressure-relief-valve-engineering-handbook-cs-cz-4262398.pdf\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">Emerson PRV Engineering Handbook<\/a>.<\/p>\n<h3>Compare the result with the applicable valve and project basis<\/h3>\n<p>Determine which outlet-pressure quantities matter to the candidate and how the manufacturer represents them:<\/p>\n<ul>\n<li>built-up back pressure from the subject relieving flow;<\/li>\n<li>constant or variable superimposed back pressure;<\/li>\n<li>total back pressure during the event;<\/li>\n<li>minimum and maximum outlet pressure over the credible cases;<\/li>\n<li>any manufacturer-defined capacity correction, set-pressure correction, balancing feature, pilot limitation or configuration-specific back-pressure limit.<\/li>\n<\/ul>\n<p>A conventional direct-spring valve, balanced-bellows valve and pilot-operated valve should not be reduced to one universal table. Emerson documents different responses and correction approaches for conventional, balanced and pilot-operated designs, while LESER publishes product-specific limits and solutions. Use exact candidate data.<\/p>\n<p>For the broader valve-configuration decision after the hydraulic condition is known, use ZOBAI&#8217;s <a href=\"\/engineering\/back-pressure-and-bellows\/\">Back Pressure and Bellows Guide<\/a>.<\/p>\n<h3>Revisit discharge-pipe sizing when the result is unacceptable<\/h3>\n<p>Outlet piping and valve review form an iterative engineering process. If the calculated outlet condition is unacceptable, first examine whether downstream resistance or system pressure can reasonably be reduced before converting the result into a valve-type rule.<\/p>\n<p>Possible review points include:<\/p>\n<ul>\n<li>increasing discharge-pipe flow area where technically appropriate;<\/li>\n<li>reducing unnecessary restrictions or sharp geometry changes;<\/li>\n<li>simplifying routing;<\/li>\n<li>reviewing high-loss fittings, silencers or downstream equipment;<\/li>\n<li>reassessing simultaneous-relief assumptions and shared-header boundaries;<\/li>\n<li>re-evaluating whether the selected valve architecture is compatible with the resulting outlet-pressure range.<\/li>\n<\/ul>\n<p>After a material hydraulic change, repeat the calculation. If piping changes cannot produce an acceptable condition, assess the valve configuration using exact manufacturer and project evidence rather than a generic back-pressure percentage.<\/p>\n<h3>What information should move into the engineering review or RFQ<\/h3>\n<p>A technically useful engineering or supplier review should identify, as applicable:<\/p>\n<ul>\n<li><strong>governing relief case and required relief duty<\/strong>;<\/li>\n<li><strong>outlet calculation flow basis<\/strong> and why that basis applies to the selected valve behavior;<\/li>\n<li><strong>fluid and phase<\/strong> \u2014 liquid, gas\/vapor, steam or potentially two-phase;<\/li>\n<li><strong>relieving pressure and temperature<\/strong>;<\/li>\n<li><strong>calculated built-up back pressure<\/strong> and the calculation method used;<\/li>\n<li><strong>superimposed back-pressure range<\/strong>;<\/li>\n<li><strong>total outlet back-pressure range during credible relief cases<\/strong>;<\/li>\n<li><strong>whether downstream\/header pressure is fixed or variable<\/strong>;<\/li>\n<li><strong>discharge destination, branch and common-header arrangement<\/strong>;<\/li>\n<li><strong>applicable project code\/standard and edition<\/strong>;<\/li>\n<li><strong>exact candidate valve\/configuration data<\/strong>, including manufacturer back-pressure limitations\/correction basis where relevant.<\/li>\n<\/ul>\n<p>The hydraulic calculation prepares a product-specific engineering question. It does not establish a ZOBAI model limit or product suitability that has not been confirmed by product documentation.<\/p>\n<\/section>\n<section>\n<h2>When a Simple Built-Up Back-Pressure Calculation Is Not Enough<\/h2>\n<p>The calculation workflow above is deliberately bounded. It applies only while the assumptions behind the selected hydraulic model remain defensible.<\/p>\n<h3>Flashing or two-phase relief<\/h3>\n<p>Single-phase outlet calculations should not be extended into flashing or gas\/liquid two-phase service by changing one density value. <a href=\"https:\/\/www.iso.org\/standard\/76057.html\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">ISO 4126-10:2024<\/a> addresses sizing of safety valves and bursting discs for gas\/liquid two-phase flow; the connected outlet system also needs a phase-appropriate pressure-loss review.<\/p>\n<p>If a liquid can flash materially in the valve or outlet piping, if the relieving stream is already two-phase, or if condensation changes the downstream state, select a two-phase method that is valid for the actual scenario and pressure range.<\/p>\n<p>The governing project method still has to be established. Referencing an ISO document does not make it the mandatory legal basis for every jurisdiction or project.<\/p>\n<h3>Interacting relief devices and complex common headers<\/h3>\n<p>A branch-level calculation also becomes insufficient when its downstream pressure is controlled by interacting relief flows.<\/p>\n<p>Escalation is appropriate when:<\/p>\n<ul>\n<li>several pressure-relief devices may relieve during the applicable scenario;<\/li>\n<li>their combined flows materially alter shared-header pressure;<\/li>\n<li>the terminal disposal system controls the branch condition;<\/li>\n<li>pressure varies enough that a fixed downstream boundary is not defensible;<\/li>\n<li>compressible network interaction, flare-system pressure, condensation or other system effects couple the branches.<\/li>\n<\/ul>\n<h3>Cases where the hydraulic assumptions are no longer defensible<\/h3>\n<p>Reassess or escalate the method if:<\/p>\n<ul>\n<li>the fluid phase is uncertain;<\/li>\n<li>significant flashing or condensation is possible;<\/li>\n<li>required thermodynamic properties are unavailable;<\/li>\n<li>a critical-flow condition cannot be represented by the selected model;<\/li>\n<li>the downstream\/superimposed pressure cannot be established for the governing case;<\/li>\n<li>the outlet-flow basis is uncertain for the selected valve behavior;<\/li>\n<li>the result materially depends on an assumption that has not been technically justified.<\/li>\n<\/ul>\n<p>Missing engineering information should remain visible as an unresolved input rather than being replaced by an optimistic assumption simply so the calculation can continue.<\/p>\n<h3>Escalate to a more appropriate system-level analysis<\/h3>\n<div class=\"zobai-decision-path\">\n<p><strong>Built-up back-pressure calculation can proceed when:<\/strong><br \/>\n  defensible fluid model + defined valve\/outlet flow basis + known discharge path + defined downstream condition<\/p>\n<p><strong>Use a more appropriate specialist or system-level analysis when:<\/strong><br \/>\n  two-phase\/flashing behavior + interacting common-header hydraulics + variable\/unresolved downstream boundary + unsupported valve-flow assumption<\/p>\n<\/div>\n<p>A built-up back-pressure calculation is most useful when its boundary and assumptions are explicit. Its role is to produce a defined hydraulic result that can be handed to the valve, piping and project review\u2014not to claim that the complete pressure-relief system has been proven acceptable.<\/p>\n<\/section>\n<section aria-labelledby=\"built-up-back-pressure-faq\">\n<h2 id=\"built-up-back-pressure-faq\">Frequently Asked Questions About Built-Up Back Pressure<\/h2>\n<h3>What is the difference between built-up and superimposed back pressure?<\/h3>\n<p>Built-up back pressure is generated by relieving flow through the valve and downstream piping. Superimposed back pressure exists at the valve outlet before the subject valve opens because of other downstream-system pressure. During relieving, the valve can experience both components together.<\/p>\n<h3>Is total back pressure the same as built-up back pressure?<\/h3>\n<p>No. LESER&#8217;s engineering terminology expresses back pressure as the combination of built-up and superimposed components. In a closed or common header, treating total outlet pressure as though it were entirely built-up can hide the pre-existing header contribution.<\/p>\n<h3>Should discharge piping be calculated using required relief flow or rated valve capacity?<\/h3>\n<p>Do not apply one answer to every valve. Emerson&#8217;s engineering handbook, summarizing API 521 practice, notes that rated capacity is used for some direct spring-operated PRVs while a required-capacity basis can apply to modulating pilot-operated designs. Freeze the valve operating behavior and governing method before selecting the outlet-flow basis.<\/p>\n<h3>Can I use a single-phase liquid equation for flashing liquid?<\/h3>\n<p>Not automatically. If significant flashing or gas\/liquid two-phase flow is credible, the single-phase assumptions no longer represent the physical problem. Use a two-phase method appropriate to the actual service, such as the applicable ISO 4126-10 or project method.<\/p>\n<h3>Why can a common relief header increase safety-valve back pressure?<\/h3>\n<p>A common header can impose superimposed pressure before the subject valve opens and can develop additional pressure when one or more devices relieve. If simultaneous flows materially alter header pressure, the branch and header need to be solved as an interacting hydraulic system.<\/p>\n<h3>Can excessive back pressure make a safety valve unstable?<\/h3>\n<p>Yes, depending on valve design and service. Manufacturer engineering guidance identifies possible effects that include lift instability or chattering, changes in set\/reseat behavior and reduced actual capacity. The acceptable limit is valve- and project-specific, so it should come from the exact manufacturer and governing basis rather than a universal percentage.<\/p>\n<h3>What information is needed to check built-up back pressure?<\/h3>\n<p>At minimum, define the relief case, outlet-flow basis, fluid\/phase, relieving pressure and temperature, valve flow data required by the method, complete discharge-path geometry and resistance, elevation where applicable, downstream pressure boundary, and any simultaneous flows that can change a common-header pressure.<\/p>\n<h3>When should a simple branch calculation be escalated?<\/h3>\n<p>Escalate when phase behavior is uncertain, flashing\/two-phase flow is important, downstream pressure is not fixed, multiple PRVs interact through a common header, critical-flow behavior cannot be represented, or the result depends materially on an unsupported assumption.<\/p>\n<\/section>\n<aside class=\"zobai-cta\">\n<p><strong>Need to review a safety valve for a defined back-pressure condition?<\/strong><\/p>\n<p>Prepare the relief duty, outlet-flow basis, fluid and phase, relieving pressure and temperature, calculated built-up back pressure, superimposed back-pressure range, total outlet-pressure range, discharge arrangement and applicable project standard. Submit those inputs through the <a href=\"\/contacts\/\">ZOBAI contact and RFQ page<\/a> for the next technical review.<\/p>\n<\/aside>\n<footer aria-label=\"Technical reference basis\">\n<p><strong>Technical reference basis:<\/strong> API 520 Part II installation guidance, API 521 relief\/disposal-system guidance, the LESER Engineering manual and its ISO 4126-9 outlet-line calculation route, ISO 4126-10:2024 for gas\/liquid two-phase sizing, and original pressure-relief-valve manufacturer engineering documentation including Emerson. Exact governing editions, product-specific back-pressure limits, correction factors and project requirements should be confirmed for the application.<\/p>\n<\/footer>\n<\/article>\n<p><script type=\"application\/ld+json\">\n{\n  \"@context\": \"https:\/\/schema.org\",\n  \"@type\": \"BlogPosting\",\n  \"headline\": \"How to Calculate Built-Up Back Pressure in Safety Valve Discharge Piping\",\n  \"description\": \"Learn how to calculate built-up back pressure in safety valve discharge piping, define the hydraulic boundary, handle liquid vs gas flow, and verify the result.\",\n  \"url\": \"https:\/\/zobai.com\/blog\/how-to-calculate-built-up-back-pressure-in-safety-valve-discharge-piping\/\",\n  \"mainEntityOfPage\": {\n    \"@type\": \"WebPage\",\n    \"@id\": \"https:\/\/zobai.com\/blog\/how-to-calculate-built-up-back-pressure-in-safety-valve-discharge-piping\/\"\n  },\n  \"inLanguage\": \"en\"\n}\n<\/script><\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u0423\u0437\u043d\u0430\u0439\u0442\u0435, \u043a\u0430\u043a \u0440\u0430\u0441\u0441\u0447\u0438\u0442\u0430\u0442\u044c \u043d\u0430\u043a\u043e\u043f\u043b\u0435\u043d\u043d\u043e\u0435 \u043f\u0440\u043e\u0442\u0438\u0432\u043e\u0434\u0430\u0432\u043b\u0435\u043d\u0438\u0435 \u0432 \u0441\u0431\u0440\u043e\u0441\u043d\u043e\u043c \u0442\u0440\u0443\u0431\u043e\u043f\u0440\u043e\u0432\u043e\u0434\u0435 \u043f\u0440\u0435\u0434\u043e\u0445\u0440\u0430\u043d\u0438\u0442\u0435\u043b\u044c\u043d\u043e\u0433\u043e \u043a\u043b\u0430\u043f\u0430\u043d\u0430, \u043e\u043f\u0440\u0435\u0434\u0435\u043b\u0438\u0442\u044c \u0433\u0438\u0434\u0440\u0430\u0432\u043b\u0438\u0447\u0435\u0441\u043a\u0443\u044e \u0433\u0440\u0430\u043d\u0438\u0446\u0443, \u0443\u0447\u0435\u0441\u0442\u044c \u0440\u0430\u0437\u043b\u0438\u0447\u0438\u044f \u043c\u0435\u0436\u0434\u0443 \u043f\u043e\u0442\u043e\u043a\u043e\u043c \u0436\u0438\u0434\u043a\u043e\u0441\u0442\u0438 \u0438 \u0433\u0430\u0437\u0430 \u0438 \u043f\u0440\u043e\u0432\u0435\u0440\u0438\u0442\u044c \u0440\u0435\u0437\u0443\u043b\u044c\u0442\u0430\u0442.<\/p>","protected":false},"author":2,"featured_media":56854,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[74],"tags":[],"class_list":["post-56802","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-sizing-performance-engineering"],"_links":{"self":[{"href":"https:\/\/zobai.com\/ru\/wp-json\/wp\/v2\/posts\/56802","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/zobai.com\/ru\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/zobai.com\/ru\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/zobai.com\/ru\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/zobai.com\/ru\/wp-json\/wp\/v2\/comments?post=56802"}],"version-history":[{"count":0,"href":"https:\/\/zobai.com\/ru\/wp-json\/wp\/v2\/posts\/56802\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/zobai.com\/ru\/wp-json\/wp\/v2\/media\/56854"}],"wp:attachment":[{"href":"https:\/\/zobai.com\/ru\/wp-json\/wp\/v2\/media?parent=56802"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zobai.com\/ru\/wp-json\/wp\/v2\/categories?post=56802"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zobai.com\/ru\/wp-json\/wp\/v2\/tags?post=56802"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}