Pressure Reducing Station

The Kv of the reducing valve, and the capacity the downstream safety valve must pass if the reducer fails open.

Unit system

Inputs

Duty flow

Upstream pressure (absolute)

Downstream pressure (absolute)

Safety valve set pressure (absolute)

Above the downstream pressure and below the design pressure of the downstream equipment.Rated Kv of the selected valve (fully open)

Comes from the catalogue. The fail-open flow is computed with THIS value, not with the Kv required for the duty.Safety valve Kdr

Reducing valve style

Kv required for the reducer

10.92

Fail-open flow — the safety valve must pass this

2,931kg/h

Cv required for the reducer	12.62
Fail-open flow ÷ duty flow	1.47
Safety valve required area	0.001264 m²
Safety valve equivalent bore	40.11 mm
Flow regime in the reducer	Choked flow at duty

The fail-open flow uses the valve’s FULLY OPEN rated Kv. Using the duty Kv would undersize the safety valve — the valve is throttled at duty, not in failure.
A rising downstream pressure REDUCES flow; what enlarges the fail-open flow is the fully open port, not the back pressure.
The safety valve area assumes 10 % overpressure and discharge to atmosphere.

A PDF carrying the inputs, results, assumptions and the source. A one-time code is sent to your address.

Results are for engineering pre-assessment and are not a product selection commitment. Final responsibility rests with the user.