Gate Valve thrust & torque calculation method 5

[siavash1111]

Hello

I am looking for some formula on thrust and torque calculation method for various type of Gate Valve (Through Conduit, block &bleed , wedge , knife , Parallel …)
Does everybody now how can I calculate below information for gate valve ?

Open Thrust
Close Thrust
Open torque
Close torque
Run torque


Thanks
Best Regards
Siavash

 

[gerhardl]

Anyone with practical experience with actuators (pneumatic, electric or others) for any type of valve, will probably advice you that if you have or find a calculation method, the results will vary upwards with, at least, from one to five times the calculated result.

Even if you bind yourself to exact same type, manufacturor (eg equal materials, accuracy, construction etc) the result will again vary with fluid type, pipeline construction, flow, pressure, impurities, age etc.

This is also the reason that suppliers wich build on actuators are asking the factories recommondation for actuator size, and answers are limiting operation conditions including fluid.

The factories recommondation will often have included a safety factor up to 50% even then.

Torque limit switches are a standard for good electrical actuators, and newest type of actuators are electronically able to log torque and operation history.

This is all for a reason: it is impossible to calculate all possible influences over a valves lifetime regarding wear and use.

Torque calculation would only be a very, very rough indication, and the simplest method is to measure.

 

[reverman]

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