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Gate Valve Torque Cal - Guide

The document discusses formulas used to calculate the thrust and torque required to operate gate valves, with many of the variables having different values depending on the vendor or power plant. The thrust formula has variables for stem cross-sectional area, line pressure, packing load, seat area, differential pressure, and a valve factor. The torque formula uses the calculated thrust multiplied by a stem factor, which also has some disagreement over its calculation. Safety factors then need to be added to the baseline values.

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Tracy Patel
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763 views1 page

Gate Valve Torque Cal - Guide

The document discusses formulas used to calculate the thrust and torque required to operate gate valves, with many of the variables having different values depending on the vendor or power plant. The thrust formula has variables for stem cross-sectional area, line pressure, packing load, seat area, differential pressure, and a valve factor. The torque formula uses the calculated thrust multiplied by a stem factor, which also has some disagreement over its calculation. Safety factors then need to be added to the baseline values.

Uploaded by

Tracy Patel
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOCX, PDF, TXT or read online on Scribd
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The formula has many variables that vary from vendor to vendor but also even many power

plants
have their own values for several variables in the formula:

Thrust (lbs) = [StA]*[LP] + [PL] + [SA]*[VF]*[DP]

StA = STem cross sectional Area

LP = Line Pressure

PL = Packing Load. This is a value that will vary vendor to vendor and is dependent on valve size.
Typically we use values from 1000 lbs to 4000 lbs depending on valve size and pressure class

SA = Seat Area

DP = Differential Pressure the valve is opening/closing against

VF = VALVE FACTOR. This is the most controversial subject around gate valves. Generically a 5° wedge
gate valve uses a 0.3 factor however you will have many Nuclear power plants that argue for
anywhere from 0.4 to 0.6 for this value depending on service. If you use a steeper wedge like 3° or
less their is a strong argument that this value should be even higher. For parallel slide valves we
typically use a 0.2 however I have never seen any consensus on this value. We have been using it for
years and haven't had a problem with undersized operators so it seems to work for us.

Torque (ft-lbs) = [Thrust] * [SF]

SF = STEM FACTOR, this is dependent on the type of stem threads you use. Be aware that there is
some disagreement also on stem factor calculations in the industry also. Many stem factor
calculations will use a coefficient of friction of 0.15 while many power plants (and also myself) think
this is too small and a 0.20 COF should be used when calculating stem factor.

These formulas get you a baseline torque and thrust value with no safety factor. You'll need to add an
appropriate safety factor for your service

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