ZBA21 Series External Thread Low-Lift Safety Valve
Spring Low Lift External Thread Safety Valve for small pressure equipment and pipelines requiring compact overpressure protection. Key selection data include DN15-DN25, PN16, PN25, PN40, PN64 and PN100 for A21H/W; PN16, PN25 and PN40 for A21F, A21H/W: up to 200 deg C; A21F: up to 80 deg C, materials, connection standard and set pressure.
Final set pressure, certified relieving capacity, material code and connection standard must be confirmed on the approved datasheet before purchase.
- Size range: DN15-DN25
- Pressure rating: PN16, PN25, PN40, PN64 and PN100 for A21H/W; PN16, PN25 and PN40 for A21F
- Temperature: A21H/W: up to 200 deg C; A21F: up to 80 deg C
- Connection: External threaded inlet/outlet
- Media: Air, ammonia, petroleum gas, corrosive gas or liquid, liquefied gas and petroleum gas depending on H/W/F configuration
- Drawings, test records and material documents confirmed for the ordered configuration.
Technical Specifications and Selection Data
Product Model
ZBA21H/ZBA21W-16/25/40/64/100 C/P/R; ZBA21F-16/25/40 C/P/R
Size Range
DN15-DN25
Pressure Rating
PN16, PN25, PN40, PN64 and PN100 for A21H/W; PN16, PN25 and PN40 for A21F
Temperature Range
A21H/W: up to 200 deg C; A21F: up to 80 deg C
Applicable Media
Air, ammonia, petroleum gas, corrosive gas or liquid, liquefied gas and petroleum gas depending on H/W/F configuration
Connection Type
External threaded inlet/outlet
Standards and Compliance
GB/T 12241, GB/T 12242 and GB/T 12243 for safety valve design, performance and test references; model coding follows the JB/T 308 valve model method where applicable.
Engineering Insight: Model Logic and Application Boundary
Model code: A21 = safety valve with external thread connection and low-lift spring structure. H/W/F identify sealing or material configuration; pressure digits identify PN rating; C/P/R identify body material code.
Typical application: small pressure equipment and pipelines requiring compact overpressure protection
Capacity review: Main connection dimensions are listed on the source catalog page. Discharge capacity and orifice sizing should be confirmed by set pressure, medium, temperature and applicable code.
This product family should not be selected from model code, nominal size or pressure class alone. Confirm the relieving scenario, required capacity, set pressure, operating margin, temperature, back pressure and actual connection standard.
Dimensions and Selection Guide
The table below is transcribed from catalog page 15. Verify critical dimensions against the approved order drawing before fabrication or piping release.
| Type / Model | Nominal Diameter (DN) | do | d | DO | M | d1 | D1 | L | L1 | Approx. H |
|---|---|---|---|---|---|---|---|---|---|---|
| A21H/W/F-16/25/40C/P/R | 15 | 12 | 15 | 20 | M27x1.5 | G1/2" | 30 | 35 | 74 | |
| A21H/W/F-16/25/40C/P/R | 20 | 16 | 20 | 25 | M33x1.5 | G3/4" | 34 | 40 | 87 | |
| A21H/W/F-16/25/40C/P/R | 25 | 18 | 25 | 31 | M39x1.5 | G1" | 44 | 52 | 100 | 105 |
| A21Y/W-64/100C/P/R | 15 | 10 | 15 | 25 | M36x1.5 | G1" | 44 | 52 | 100 | 105 |
| A21Y/W-64/100C/P/R | 20 | 10 | 20 | 31 | M39x1.5 | G1" | 44 | 52 | 100 | 105 |
| A21Y/W-64/100C/P/R | 25 | 12 | 25 | 31 | M42x1.5 | G1" | 44 | 52 | 100 | 105 |
RFQ checklist
RFQ checklist: model or valve type, DN/NPS, PN/Class, set pressure, relieving medium, operating temperature, body and trim material, inlet/outlet connection standard, cap/lever/pilot options, quantity, drawing, certificate and inspection requirements.
Failure Analysis, Manufacturing Evidence and Quality Control
Common misapplication risks: incorrect thread or connection standard, insufficient certified relieving capacity, unsuitable body or trim material, operating pressure too close to set pressure, unreviewed back pressure, and installation loads transferred to the valve.
Material review: body materials: WCB carbon steel, ZG15Cr1Mo alloy steel, ZG15Cr1Mo1V/ZG20Cr1Mo1V high-temperature alloy steel, CF8/304, CF8M/316 or CF3M/316L according to model body code and service. Trim and internals: 20Cr13, 304, 316, 316L or alloy trim according to body code and medium; corrosive or high-temperature service can use stainless or alloy internals. Spring and stem: 50CrVA spring for standard service; stainless or coated fluoroplastic/304 spring options for corrosive service where specified.
Testing and inspection: Set pressure calibration, shell strength test, seat tightness/leakage test, reseating/blowdown check, dimensional inspection and material verification can be supplied according to the confirmed standard and order requirements.
Source and scope: product data is based on Zobai Safety Valve Product Catalog.pdf, catalog page 15. Project compliance remains subject to the approved datasheet, drawing, calculation and controlled certificates for the ordered configuration.
Review material traceability, type-test scope and project certificate requirements.
Related Products
FAQ
Safety Valve FAQs
What models are covered by this ZBA21 External Thread Low-Lift Safety Valve page?
ZBA21H/ZBA21W-16/25/40/64/100 C/P/R; ZBA21F-16/25/40 C/P/R
What size, pressure and temperature data should be confirmed?
Size: DN15-DN25. Pressure: PN16, PN25, PN40, PN64 and PN100 for A21H/W; PN16, PN25 and PN40 for A21F. Temperature: A21H/W: up to 200 deg C; A21F: up to 80 deg C. Confirm the exact combination for the selected model.
Which media can this product family handle?
Air, ammonia, petroleum gas, corrosive gas or liquid, liquefied gas and petroleum gas depending on H/W/F configuration. Material and sealing compatibility require review for the actual fluid composition and temperature.
Can the catalog dimension table be used for final fabrication?
Use it for preliminary review only. Confirm critical dimensions, connection details and orientation on the approved order drawing before piping or equipment fabrication.
What should be included in the RFQ?
RFQ checklist: model or valve type, DN/NPS, PN/Class, set pressure, relieving medium, operating temperature, body and trim material, inlet/outlet connection standard, cap/lever/pilot options, quantity, drawing, certificate and inspection requirements.