# How to use flow rates (GPM) and pressure drop to determine if a valve is usefull

• MoonKnight
In summary, the valve can handle a flow rate of 50 GPM, and the pressure drop is around 0-145 psi. The valve is a 2/2 Way, Normally closed, w/ 2-pilot control, and coupled solenoid.
MoonKnight
I need to determine if a valve can handle a flow rate of 50 GPM, this valve being: 2/2 Way, Normally closed, w/ 2-pilot control, and coupled solenoid.

I also need to determine pressure drop...

it is a burkhert model - 457361D

the valve specs indicate:

Cv = 35.1

pressure measurement = 0 -145 psi

if anyone can help, or push me in the right direction, thanks...

The Cv is your main source of information. The Cv is, by definition, the amount of flow through the valve with a delta P across it of 1 psi. Most valve suppliers will give you a curve of Cv vs. % open. You can use the following equation to calculate the flow through given the following equation:

$$Cv = Q \sqrt{\frac{SG}{\Delta P}}$$

The equation given is generally correct as long as there is no choking, and the flow is laminar.

The ISA standard S75.01.01 gives extensive information on the subject. Also, the valve manufacturer should provide sizing information that will take that into account.

www.ostand.com

ooops I meant to say the flow must be TURBULENT.

proinwv said:
The equation given is generally correct as long as there is no choking, and the flow is laminar.

The ISA standard S75.01.01 gives extensive information on the subject. Also, the valve manufacturer should provide sizing information that will take that into account.

www.ostand.com

proinwv said:
ooops I meant to say the flow must be TURBULENT.

I've never heard of a restriction on the flow being turbulent for that equation to be valid. Where did you reference that from?

CS

It is part of the ISA S75.01.01 This is "the" standard of the valve industry.

Most references ignore this at their peril. Choking occurs when the pressure in the vena contracta within the valve drops to the vapor pressure of the liquid and vaporization occurs, preventing further flow increases, unless the inlet pressure is increased.

Turbulent flow rather than laminar or transitional will pass the amount indicated by the equation that was quoted earlier. Otherwise the equation must be modified by a valve reynolds number factor which is =<1. Turbulent flow occurs when the valve reynolds number is 10,000. This is calculated by the equations in the ISA standard.

If these factors are not checked for signifcant errors can occur in the calculation of flow or delta p.

This might be of some use in understanding what I was trying to say, as it relates to turbulent flow.

#### Attachments

• ISA basics.xls
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thanks for your help guys... I found what I needed a while ago, but your responses were appreciated

## What is a flow rate (GPM)?

A flow rate, also known as gallons per minute (GPM), is a unit of measurement used to determine the volume of fluid that can pass through a valve in a given amount of time.

## What is pressure drop?

Pressure drop is the decrease in pressure that occurs when fluid flows through a valve. It is measured in units of pressure, such as pounds per square inch (psi) or kilopascals (kPa).

## How do flow rates and pressure drop affect the usefulness of a valve?

The flow rate and pressure drop are important factors in determining the effectiveness of a valve. A valve with a high flow rate and low pressure drop will be more efficient and useful in controlling the flow of fluid.

## How can I use flow rates and pressure drop to determine if a valve is useful?

To determine if a valve is useful, you can compare the flow rate and pressure drop of the valve to the desired flow rate and pressure drop for your specific application. If the valve can meet the required flow rate with an acceptable pressure drop, then it can be considered useful.

## Are there any other factors to consider when using flow rates and pressure drop to determine the usefulness of a valve?

Yes, there are other factors that may affect the usefulness of a valve, such as the type of fluid being used, the temperature and viscosity of the fluid, and the overall design and condition of the valve. It is important to take all of these factors into account when evaluating the usefulness of a valve.

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