When debris, such as scale, rust and other matters mix with water, oil, gas, air, steam or other media and is allowed to flow through a pipeline, it can become the cause of damage to the line’s valve seats, resulting in shortened valve life, not to mention equipment malfunction and damage. Therefore, Use of rightly selected strainers at correct locations is a must to protect expensive and critical downstream equipment such as pumps, flow meters, steam traps, control valves etc. in this article, Linquip has compiled necessary information on strainer valve. Read on to find out more about strainers and their application within a system.
What is a strainer valve?
Strainer valve can be defined as a pipe fitting through which liquid is passed for purification, filtering or separation from solid matter; anything used to strain a liquid; any device functioning as a sieve or filter used to prevent solid bodies from mixing in a liquid stream or flow line. Strainers arrest pipeline debris such as scale, rust, jointing compound and weld metal in pipelines, protecting equipment and processes from their harmful effects, thus reducing downtime and maintenance.
Different types of a strainer valve
Strainers can be classified into two main types according to their body configuration:
- T-Type or Basket Type
A Y Strainer valve takes its name from its configuration and is most commonly used in pressurized lines, gas or liquid. They can also be used in suction or vacuum conditions. Y-Strainers are intended for applications where small amounts of solid particulate are expected and where clean-out will be infrequent. If solids are flushed easily from the screen, and fluid can be exhausted to atmosphere, a blow-down valve on the drain port will allow clean-out without removal of the screen and without interrupting the process flow.
A Y-Strainer has the advantage of being installed in either a horizontal or vertical position. Obviously, in both cases, the screening element must be on the down side of the strainer body so that the entrapped material can be properly collected in it.
In horizontal steam or gas piping, Y type strainer should be installed in such a manner so that the pocket is in the horizontal plane. This stops water from collecting in the pocket which can cause erosion and affect heat transfer processes.
In liquid systems, the pocket should point vertically downwards. This ensures that the removed debris is not drawn back into the upstream pipework during low flow conditions.
Although it is recommended to install strainers in horizontal lines, this is not always possible, and they can be installed in vertical pipelines if the flow is downwards, in which case the debris is naturally directed into the pocket.
Some manufactures reduce the size of the Y -Strainer body to save material and cut the cost. Before installing a Y-Strainer, be sure it is large enough to properly handle the flow. A low-priced strainer may be an indication of an undersized unit.
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T-Type or Basket Type Strainer Valve
T type or Basket type or Pot type strainer is defined by a vertically orientated chamber, typically larger than that of a Y-type strainer. Size for size, the pressure drop across a basket strainer is less than that across the Y-type as it has a greater free straining area, which makes the basket type strainer the preferred type for liquid applications. As the dirt holding capacity is also greater than in Y-type strainers, the basket type strainer is also used on larger diameter steam pipelines.
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Basket type strainers can only be installed in horizontal pipelines, and for larger, heavier basket strainers, the base of the strainer needs to be supported.
To service a basket type strainer, the cover can be removed so technicians get immediate access to the filtering element if it needs replacement (due to accumulated debris). When basket type strainers are used on steam systems, a significant amount of condensate may be formed. Consequently, strainers designed for use in steam systems usually have a drain plug, which can be fitted with a steam trap to remove the condensate.
Strainer Valve Material
The most common material used for Y type strainers and Basket strainers bodies are cast iron, bronze, carbon steel, stainless steel, and plastic.
Cast iron is the most popular strainer body material because of its low initial cost. It is used in systems where the pressure and temperature of the water are not high and the system is not subject to high thermal or mechanical shock. Cast iron is mostly used for larger size potable water lines and many non-potable water systems in addition to a variety of other product and process uses.
Bronze material is preferred for brackish, saline, and seawater service. It is often used for potable water services. Its cost doubles that of cast iron.
Carbon steel material is used where high temperature and pressure conditions are encountered and where resistance to thermal and mechanical shocks is required. Carbon steel components are the materials of choice where fire hazards exist.
Chrome-Moly steel material is used for high pressures and temperatures.
Stainless steel is the preferred body, basket, and screen material because of its resistance to corrosion and contamination and ease of cleaning.
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Differences between Strainer Valves and Filters
A filter is a device that removes particles from a liquid or gas. It consists of a disposable medium to remove particles of specified micron sizes. All strainers are filters, but not all filters are strainers. A strainer is only one type of filter. Strainer valve uses a perforated plate or screen mesh to remove larger particles from a process stream. The major advantage of a Strainer is that it is reusable. The filter screen is only used once and must be changed when it is clogged.
The main difference seems to be in diameter of the holes in the media screen also termed as mesh size in case of strainer. There is no hard and fast size division to define strainers from filters.
Another difference is resistance. Strainers normally present low resistance to liquid flow. The pressure drop across most strainers is relatively small compared to the pressure drop across thick media filters or membrane filters.
Last but not least, is their function. A strainer is used to protect other downstream equipment from damage by rogue junk. A filter is employed to separate particles from the fluid.
So, this is all you need to know about strainer valve and its different types. Now it is your turn to share your experience with us in the comment section. Is there any question regarding the topic? Feel free to sign up on Linquip website where our experts are prepared to give you the professional advice you need.
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