DR20 Direct-Acting Pressure Reducing Valve

Mechanism for Countering Outlet Pressure Drop

• If the outlet pressure drops, the force applied to the large coil spring by the bellows weakens.
• As a result, the large coil spring expands and the bellows pushes the main valve down.
• This makes the main valve open wider and let more steam pass through. The increase in steam volume makes the outlet pressure increase and restores original pressure levels.

Mechanism for Countering Outlet Pressure Increase

• If the outlet pressure increases, the bellows applies more force to the large coil spring.
• As a result, the large coil spring contracts and the small coil spring pushes the main valve up.
• This makes the main valve shut tighter and let less steam pass through. The decrease in steam volume makes the outlet pressure decrease and restores original pressure levels.

Mechanism for Countering Inlet Pressure Drop

• If the inlet pressure drops, the difference in pressure between the inlet and outlet of the valve decreases, and so the upward force pushing the valve shut also decreases.
• This makes the main valve open wider and allow more steam to pass through, and so the outlet pressure increases.
• When the outlet pressure increases, the force that the bellows applies to the large coil spring strengthens.
• As a result, the large coil spring contracts and the main valve shuts tighter.
• Because of this, less steam passes through the valve. The decrease in steam on the outlet side makes the outlet pressure drop, restoring original pressure levels.

Mechanism for Countering Inlet Pressure Increase

• If the inlet pressure increases, the difference in pressure between the inlet and outlet of the valve also increases, and so the upward force pushing the main valve shut increases.
• This makes the main valve shut tighter and allow less steam to pass through, and so the outlet pressure decreases.
• When the outlet pressure decreases, the force that the bellows applies to the large coil spring weakens.
• As a result, the large coil spring expands and the main valve opens wider.
• Because of this, more steam passes through the valve. The increase in steam on the outlet side makes the outlet pressure increase, restoring original pressure levels.