Specifying Valves

Table of Contents

Overview

The most relevant parameters to consider when selecting a valve are its application, the valve actuation [1]

Application:

When first choosing a valve type, it is important to consider the application you are using it for. Here are some questions to think about:

• What media will be flowing through your valve? 

• How will the flow of the medium of your valve be controlled?

• What is the function of the valve you are going to use?

Valves may be used for start-stop operations or for throttling. The type of valve selected changes significantly depending on these two parameters. An aspect to consider is water hammering, which is defined as a pressure variation triggered by an abrupt change in the fluid flow [1]. A reasonable approach to choose a valve is to make sure it will reduce water hammering effects on the pipe. Other aspects to consider will be pipe size, flow rates and the pressure used. The nature of the flow in the pipe will determine the type of valve required for certain purposes.

Valve actuation.

Different types of valves are offered depending on the users needs. They may be pneumatic, electric, hydraulic. Other type of valves are check valves and ball valves [2]. The nature of the flow in the pipe, for example,  will determine the type of valve required for certain purposes. For example, a globe valve becomes useful when dealing with a fluid with uninterrupted path.

Check out the Valves wiki page to learn more about the type of valves.

Flow regulation considerations

Regulating flow rates is the main reason reason why valves are used. Therefore, flow considerations are crucial when selecting a valve. These are some valve duties to consider:

• Valves for stopping and starting flow: These valves can be selected for low flow resistance and straight flow passage. These valves should be an option when there is no need for working under specific flow rate. Slide valves, rotary valves, and flex body valves could be used for this duty [3].
• Valves for controlling flow rate: The valve operation may become more complicated when throttling control is needed. Methods to achieve such control are closing down, sliding, and rotating valves. The valve to use will depend on the method chosen. Globe valves, parallel gate valves and ball valves are valid options to obtain flow control using one of these methods respectively [3].
• Valves for diverting flow: Sometimes, the fluid needs to flow into more than one direction. Plug valves and ball valves with three or more ports can be selected for this duty [3].

A chart displaying different valves and modes of flow regulation is presented as a guide to consider when thinking about specifying valves [3]

Valve Material

What media will be flowing through your valve? What is its state? Is the system corrosive or abrasive? Choosing the material for your valve will greatly depend on the media flowing through it since they both have to be compatible.

Common types of valve materials:

• Stainless Steel - saltwater, acids

• Brass/Bronze - VOCs (volatile organic compounds), solvents, fuels

• Plastic - VOCs, solvents, fuels

Visit ScienceDirect for more information on various materials and their applications. For information on materials related to specific types of valves, visit each valve page from Valves.

Nature of flow

It is crucial to consider the nature of the flow when selecting a valve. Relevant properties are flow phase, density, and compressibility. The valve selected should be able to withstand the pressure, temperature and corrosion characteristics of the fluid [4]. The following chart presents a guide when choosing valves based on the nature of the flow:

Temperatures and Pressures

A useful guide to check for pressure and temperature regulations is CRN (Canadian Registration Number). Having a CRN ensures the design has been accepted and registered in a provincial territory when the pressure is above 15 psi . If the valve you need to use does not have such pressure, CRN becomes irrelevant.

Valve Data Sheets

Valve data sheets are useful documentation to define valve specifications necessary to know to select a valve. The sheet provides information on design conditions, materials of construction, and valve dimensions. Therefore, VDSs provide with relevant points to consider to select a valve. An example of a Valve Data Sheets for a check valve is provided below [5]:

Connection Type

More information on Connection Types and End Connections can be found on the Connection Types page.

Selecting a valve checklist

1.-  Understand the function the valve will play.

2.- Identify the flow regulation needed.

3.- Recognize the nature of the flow

4.- Check for valve material and media flowing compatibility.

5.- If the valve has a 15 psi pressure or above, research the valve CRN

6.- Read the valve specifications in the valve data sheets

Valve Dimensions

ID vs OD

Handle Length

Control

Manufacturing Outside of Canada

References

Contributors: Israel Moya