Spirax Sarco 25PRV Pressure Reducing Valve Operation

A properly designed steam system is extremely important. Clean, dry steam through your steam distribution network maximizes the quality of steam, and protects all related components thus keeping costs and maintenance to a minimum.

Principles of Operation of the Pressure Reducing Valve: - Normal positions before start-up are with the main valve closed and the pilot valve held open by spring force or air pressure. Entering steam passes through the pilot valve into the main diaphragm chamber and also out through the control orifice. As flow through the pilot valve exceeds flow through the orifice, control pressure increases in the diaphragm chamber and opens the main valve. As steam flows through the main valve, the increase in downstream pressure feeds back through the pressure sensing line to the underside of the pressure diaphragm. When the force below that diaphragm balances the compression force of the spring above it, the pilot valve throttles. The control pressure maintained in the main diaphragm chamber positions the main valve to deliver just enough steam for the desired delivery pressure. Adjustment of the spring or air pressure above the pressure diaphragm changes the downstream pressure set point. When steam is no longer required, the sensing line pressure increases closing the pressure pilot and the control pressure bleeds back through the control orifice. This allows the main valve to hold the desired reduced pressure, and it may close tight for a dead-end shutoff.

Operation of the Spirax Sarco Model 25PRV Pressure Reducing Valve

0:0:24 No Flow Conditions
0:0:27 Steam Flow Begins
0:0:29 Progresses Toward Equilibrium
0:0:35 Attains Set Point
0:0:43 Increased Downstream Load
0:0:56 Elevated Setpoint
0:1:09 Downstream Shutoff
0:1:19 The Spirax Sarco Model 25PRV Features

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