Pressure Reducing Valves Β· Pressure Relief / Sustaining Valves
Pressure Relief and Sustaining Valve
The pressure relief and sustaining valve is the pilot-controlled execution of the pressure reducing family that guards upstream pressure: it stays closed while upstream pressure is above set-point and modulates open to spill flow and hold a minimum upstream (sustaining) level, with the same pilot loop serving pure relief duty against surges. The benchmark execution covers DN50 to DN600 flanged sizes at PN1.6/2.5/4.0, with body and disc in cast iron, ductile iron, carbon steel or stainless steel, an EPDM or NBR diaphragm, stainless SS304 spring and shaft, and a stainless steel or brass pilot valve.
Part of the Pressure Relief / Sustaining Valves family
Last updated: 2026-11
Specifications
| pressure class | PN1.6, PN2.5, PN4.0 |
|---|---|
| body | Cast Iron, Ductile Iron, Carbon Steel, Stainless Steel |
| diaphragm | EPDM, NBR |
| disc | Cast Iron, Ductile Iron, Carbon Steel, Stainless Steel |
| pilot valve | Stainless Steel, Brass |
| spring | SS304 |
| shaft | SS304 |
| dimensions size mm | 50-600 (50,65,80,100,125,150,200,250,300,350,400,450,500,600) |
| length l mm | 205-1230 per size |
| height h mm | 270-1370 per size |
| height h1 mm | 200-950 per size |
Application & selection guidance
Select this execution where a minimum upstream pressure must be held while excess flow spills - pump discharge sustaining, zone back-pressure control, or surge relief on DN50 to DN600 mains. Confirm the working pressure class (PN1.6, PN2.5 or PN4.0) covers the worst upstream case, pick body and disc material against the medium, verify the diaphragm compound (EPDM or NBR) suits the fluid and temperature, and match the per-size face-to-face and height dimensions tabulated for the selected DN against the installed pipework envelope.
Frequently asked questions
How does a pressure relief and sustaining valve differ from a standard pressure reducing valve?
A reducing valve senses and holds a steady downstream pressure; a relief and sustaining valve senses upstream pressure, staying closed while upstream pressure is above set-point and modulating open to spill flow so the minimum upstream (sustaining) level is held. The same pilot-controlled main valve can therefore serve back-pressure sustaining duty and pure relief duty against surges.
Which materials are used in the pressure boundary and trim?
The benchmark page lists body and disc in cast iron, ductile iron, carbon steel or stainless steel, a diaphragm in EPDM or NBR, a pilot valve in stainless steel or brass, and SS304 for the spring and shaft. That spread lets the execution be matched to water duties across PN1.6, PN2.5 and PN4.0 systems from DN50 to DN600.
What information is needed to quote a pressure relief and sustaining valve?
Nominal size within DN50 to DN600, the working pressure class (PN1.6, PN2.5 or PN4.0) against the line rating, the upstream set-point to sustain or relieve, medium and temperature so the EPDM/NBR diaphragm and body material can be confirmed, and the per-size face-to-face (L), height (H/H1) envelope from the dimension table against the mating pipework.
Ordering & documentation
Documents
Ask for the documentation set you need with the inquiry β typical items for this execution (material certificates, test reports to the listed inspection standard, dimensional drawings) are confirmed and supplied with the quotation.
Quotation
A quotation-ready inquiry states: nominal size and pressure rating, body and seat material preference, end connection, operation, and the service medium with temperature. Typical values on this page are benchmark reference ranges; the binding values are confirmed at quotation.
Sample & supply
Supply terms, order quantities and lead time are agreed per order β state the destination country and required schedule with the inquiry.
Storage & shipping
Store valves with seats and seals protected from UV, ozone and deformation, keep end-face protectors on until installation, and for elastomer- or PTFE-seated executions avoid prolonged outdoor storage β seat compounds age fastest in direct sunlight and freezing conditions.
More in the Pressure Reducing Valves family
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