Sentry Equipment - Sampling Systems - Sampling Equipment

Telephone:  +1-262-567-7256

Back Pressure Regulator/Relief Valve

Maintain constant pressure and analyzer flow

The Sentry® Back Pressure Regulator/Relief Valve (BPRV) maintains constant pressure and constant analyzer flow while protecting critical sampling components as a relief valve. The Sentry BPRV relief valve holds a constant pressure of approximately 20 psig (1.4 barg) at the analyzer inlet when installed as recommended. This pressure is maintained independent of source pressure fluctuations or sample flow changes. If inlet pressure rises, the regulator opens to let excess flow pass through to drain. This flow is usually used as the grab sample. This unit also acts as a relief valve in the event of an over-pressure condition


When severe service pressure reduction is handled by a Sentry VREL® valve or needle valve, the BPRV only has to control pressure between 20 psig (1.4 barg) and atmosphere. This allows precise pressure control, minimizes plugging and ensures high reliability.

The Sentry BPRV has a much flatter response curve than the standard back pressure valve designed for general process applications. For example, if the set point flow rate is 1200 cc/min, a 25% change in the flow produces only a 0.2 psi (0.014 barg) change in upstream pressure, which is three times more sensitive than a standard back pressure regulator.

In normal operation, there is always a flow from the exhaust port. This flow increases with rising source pressures and decreases with falling source pressures. The BPRV also functions as a fail-safe relief valve, with a relieving capacity exceeding that of the most commonly used 1/4-inch relief valve. Since the BPRV is always in service, a malfunction is immediately evident, while a relief valve can freeze with no outward indication – until it fails to operate in an emergency.


  • Precise pressure reduction and control when used in conjunction with a VREL® or needle valve
  • Most effective way to assure a constant flow rate to on-line analyzers
  • Specially designed for steam/water sampling service 
  • Non-plugging design
  • Will not wire draw or erode in normal service
  • Fail safe relief valve

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Back Pressure Regulator/Relief Valve

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