Relief Valves
Source relief valves from India's verified manufacturers and exporters on Himalay. Browse the full range for industrial and export applications.
About Relief Valves
Spring-loaded pressure relief valves across 252 listed configurations — conventional and bellows types to API 526, orifice letters D through T (S excepted), in DN25, 40, 50, 80, 100, 150 and 200. Compare and submit an RFQ.
Pressure relief valves are the last line of defence on a pressure system. They open automatically when inlet pressure reaches a set point, discharge enough fluid to arrest the rise, and reseat when pressure recovers — protecting vessels, exchangers and piping against overpressure without any operator or control system involvement. Himalay lists relief valves in two designs: conventional, where the bonnet is vented to the discharge side so built-up back pressure acts on the spring, and bellows, where a balancing bellows isolates the disc from back-pressure variation so the set pressure holds even when the discharge header is shared. The catalogue spans 252 configurations in DN25, DN40, DN50, DN80, DN100, DN150 and DN200, at ASME 150, 300 and 600. All listed valves are spring-loaded with flanged connections. Orifice sizes follow the API 526 letter series — the catalogue lists D, E, F, G, H, J, K, L, M, N, P, Q, R and T. Bodies are carbon steel (A216 WCB), SS316 (CF8M) and low-temperature carbon steel (A352 LCB), with SS316 nozzle and disc trim. Design follows API 526, the purchase specification for flanged steel pressure-relief valves — which fixes orifice designations D through T (0.110 to 26.0 sq in, with the letter I omitted), inlet and outlet sizes and ratings, materials, pressure-temperature limits and centre-to-face dimensions — together with ASME Section VIII for the pressure-vessel code requirements. Relief valve selection is a calculation, not a catalogue pick: state the relieving scenario, required capacity, set pressure, back pressure and fluid properties in your enquiry.
Specifying Relief Valves: Relieving Case, Orifice, Back Pressure and Type
A relief valve is specified by calculation
Unlike an isolation valve, you cannot select one from a size and a class. The sequence is: identify the governing relieving scenario (fire case, blocked outlet, control-valve failure, thermal expansion), calculate the required relieving capacity, convert that to a required effective orifice area using API 520, then round up to the next standard orifice letter in API 526 and confirm the inlet and outlet ratings. A valve chosen on line size alone will be wrong in both directions — oversized valves chatter, undersized ones do not protect.
The API 526 orifice series
API 526 is a purchase specification: it fixes orifice designations D through T, spanning 0.110 to 26.0 square inches with the letter I omitted, along with valve size and pressure rating for inlet and outlet, materials, pressure-temperature limits and centre-to-face dimensions. That standardisation is the point — it lets valves from different manufacturers be interchanged on the same inlet-outlet combination. The catalogue lists orifices D, E, F, G, H, J, K, L, M, N, P, Q, R and T.
Conventional versus bellows
A conventional valve's bonnet is vented to the discharge side, so back pressure acts on the disc and shifts the effective set point. A bellows valve introduces a balancing bellows whose effective area equals the seat area, isolating the disc from back-pressure variation and holding set pressure in shared relief headers. Where several valves discharge into a common header, the bellows design is normally the correct one; where discharge is to atmosphere, conventional is simpler and cheaper.
Size, class and materials
DN25 to DN200 across 252 configurations, in ASME 150, 300 and 600, all spring-loaded and flanged. Bodies are A216 WCB, CF8M stainless and A352 LCB low-temperature carbon steel; trim is SS316 nozzle and disc. The −29 °C Charpy impact threshold is the conventional dividing line below which LCB replaces WCB.
Set pressure, accumulation and overpressure
Set pressure is normally at or below the protected equipment's maximum allowable working pressure under ASME Section VIII; the valve must then pass full rated capacity within the code-permitted accumulation above that pressure. These three figures — set pressure, allowable accumulation and required capacity — are what a supplier needs; the valve size falls out of them.
Conformity
PED 2014/68/EU category and module with CE marking for the EU, SABER for Saudi Arabia, ECAS for the UAE, EN 10204 3.1 certificates as the procurement baseline, and NACE MR0175 for sour service. Where the protected equipment is code-stamped, state the code-stamp requirement explicitly at enquiry stage.
From spec to RFQ
Send: relieving scenario and required capacity, fluid and phase, relieving temperature, set pressure, superimposed and built-up back pressure, inlet and outlet line sizes and ratings, body and trim requirement, and destination market. Share the relief calculation or the datasheet with your RFQ and the orifice and configuration are confirmed against the catalogue directly.
Back pressure in the enquiry
State both components: superimposed back pressure present in the header before the valve lifts, and built-up back pressure generated by the valve's own discharge through the outlet piping. Together they determine whether the conventional design's set-point shift is tolerable or a bellows valve is required.
