Basic Guidelines for Valve Selection Across Process Applications

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Basic Guidelines for Valve Selection Across Process Applications

On December 14, 2018, Posted by , In Valve, With No Comments

LVSA - Valves -Durban-Johannesburg-Capetown-Ball Valves-Butterfly-Valves-Check Valve-Neway ValvesGate, Ball and Butterfly Valves are the most common form of shut-off valve, with ball and even butterfly valves rapidly becoming the primary choice due to the ease of automation and fast shut-off abilities, and in the case of ball valves the barest minimum of flow restrictions. We are often supplying ball and butterfly valves fully actuated, as plants of today become more and more automated, and are often now run by computers and the flick of a switch.

Getting the right selection of valves across a diverse process application can be a difficult task for many design engineers, however with a step by step approach one can definitely narrow down to the most suitable valve to meet any process across variable temperature, pressure and flow media. But first of all you should know a little more about the service conditions. To identify the same you could start by listing down answers to the following questions.

1. Where the valve is to be used, what function you want to perform?
2. What are the pressure/temperature requirements?
3. What kind of fluids will be in line?
4. What size is the line?
5. Are the conditions moderate or extreme?
6. How much room have you got for valve stems/handles?
What are the service requirements, are the valves to be regularly dismantled for cleaning? Is the installation permanent, or likely to be cut into frequently?
If you can answer these questions the choice of valve becomes evident very quickly, especially to one of our experienced valve sales staff.

1. Starting and Stopping flow:
Gate, Ball and Butterfly Valves are the most common form of shut-off valve, with ball and even butterfly valves rapidly becoming the primary choice due to the ease of automation and fast shut-off abilities, and in the case of ball valves the barest minimum of flow restrictions. We are often supplying ball and butterfly valves fully actuated, as plants of today become more and more automated, and are often now run by computers and the flick of a switch.

2. Regulating Flow:
Regulating or throttling flow is most commonly done with the use of a globe valve, and to a much lesser extent an angle valve. The seat design forces the flow evenly around a disc or plug arrangement that enables a closer regulation of flow. Globe valves are often used for the control of steam. Your garden tap is a very common and basic form of a globe valve design.

3. Preventing Back Flow:
This is the function of a check valve; it prevents flow reversal in piping, a primary cause of water hammer. Check valves most commonly are swing checks, normally used with gates and ball valves, and lift check or spring checks, which are normally used with Globe and Control type valves.

4. Regulating Pressure:
Pressure Regulators and Control Valves are used to reduce incoming pressure and maintain it at a required service pressure. Fluctuations to the inlet pressures of a pressure regulator will not affect the outlet pressure for which it is set at.

5. Relieving pressure:
These are known as Safety Valves, normally used for steam, air, and gases, and Relief Valves, usually used for liquids. These are normally spring loaded valves which open automatically when the pressure exceeds a set limit. They can either vent to atmosphere or to other piping. Excessive pressures in something like a Boiler could cause major damage, if a relief valve was not used. Selection of industrial valves also depends on the functionalities required as well as service applications. Please find below a comparative chart to help you better select between a gate valve, globe valve, ball valve and butterfly valve.

Common materials valves are made with are
Brass and Bronze: Brass is the stock standard material used in most small bore, standard cold water applications. Bronze an alloy of copper, tin, lead and zinc, is normally used for steam and higher temperatures up to 230°C.
Cast Iron: Normally used for lower pressure applications and in butterfly valves bodies where it provides a cost effective alternative to steel. Common in the fire protection and water industry.
Carbon and Stainless Steel: Steel is recommended for higher pressure and temperature applications and/or in services conditions that may be too harsh for Brass, bronze and Cast iron.
Alloys: Used in severe corrosive or acidic applications, or for use at extreme temperatures. Many different types of alloys are available, but these are normally manufactured and imported as required, as some of the more exotic materials can be quite expensive to have sitting around a shelf gathering dust.
PVCs: Plastics and PVCs are becoming an alternative to brass for use in low pressure/temperature air, water and even chemical applications.
Valve markings
In addition to the maker’s brand and valve size, is a basic service rating which appears on the body of most valves. Pressure and Temp ratings are normally expressed in pounds and are in terms of steam, unless otherwise indicated.Steel ratings bear a mark such as 150, 300, 600, 900 etc. The figures denote a maximum pressure (in pounds) at a certain maximum temperature, for which the valve is suited. And will also reflect on any ANSI flanges required for the end connections.The important effect temperature has on pressure ratings means it is imperative that manufacturer’s service tables are referred to.

 

Article from Amrutha Technologies Blog,

Read More: http://amruthatechnologies.blogspot.com/2016/05/why-is-it-essential-to-have-right-valve.html

 

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