How Does Water Pressure Affect Butterfly Valves?

If its a butterfly valve, its supposed to have no effect. Because butterfly valves are balanced for actuating torque in both sides of its plate. Even flow is suposed to be balanced.

What causes more problems in those valves are things like damaged or dirty bearings, bent shafts causing misalignments, and valve plate or sealing rings stucking in the sealing diameter.

Hi bhrescobar,

Absolute pressure doesn't affect too much the torque to actuate a butterfly valve but your statement "Even flow is supposed to be balanced" is not right. As valve disk is turning from closed position to open or viceversa, as the angle between disk and flow direction is changing, appears a hydrodynamic torque which helps or opposes to the disk movement.

The minimum required actuation torque, for a butterfly valve is the largest of the following values:

1. Seating/unseating torque , or

2. Maximum total dynamic torque during opening/closing stroke

The minimum torque that the valve stem and its connections to the disc and actuator should be able to withstand is called the maximum transmitted torque, and it is the larger of:

1. The required actuation torque defined above, or

2. The peak hydrodynamic torque.

Each of these torque values consists of several components. The calculation of each torque component depends on one or more of the following factors:

• Particular valve design

• Valve operating conditions: pressure, temperature, differential pressure, fluid media, and flow rate at various disc opening angles

• Valve installation and orientation in the piping system

• Hydraulic system characteristics

And take into account that if valve needs to be tight seated (no modulating/throttling service) differential pressure across the valve is important to calculate the seating torque needed.

Another aspect which affect the required torque is the disk type (symmetric, single, double or triple offset) and the relative position of disk and flow.

Kind regards