Y-Strainers for Pipes

The size of the openings through a screen is referred to as mesh, and the size of the openings through a basket is referred to as perforations. The term mesh describes a screen that uses a woven wire cloth manufactured from the material chosen for the intended service.

The most common material for all applications is stainless steel. Mesh screens are generally available in standard sizes (from 20 to 200 mesh).

The mesh size does not indicate the particle size retention since the size of the mesh opening is determined by the diameter and number of wires/inch. For example, an 80 mesh means 80 vertical and 80 horizontal strands of wire per inch.

For critical applications, a screen should be selected on particle retention capability (not mesh size). Standard perforated screens are manufactured (from light or heavy gauge sheet metal) available in standard sizes.

The baskets should be assembled by either welding or brazing. The strongest are of welded construction.

Solder is much weaker and easy to break. If a basket strainer is required for fine straining, it is common practice to add a wire mesh liner inside the perforated bucket since the screen alone is too weak to provide the necessary mechanical strength.

The material to be used depends both on the intended water service and the body that the strainer is installed into.

The most usual of basket materials are brass and stainless steel.

Cast iron strainer bodies usually use baskets of brass and stainless steel, depending on the service. Bronze bodies generally require Monel metal baskets because of the severe service. Stainless steel baskets are used with stainless steel bodies. The baskets are made, in general, from sheet metal with a wide variety of diameter perforations.

A Y-strainer is generally furnished with 1⁄16-in perforations in sizes up to 4 in, 1⁄8-in perforations in larger sizes for liquid service, and 3⁄64-in perforations for steam service. If finer straining is required, a wire mesh screen fitted inside a basket is used.

In this case, generally accepted practice limits the perforations in the basket to 50 percent of the wall area in order not to lose strength.

This combination provides an excellent ratio of maximum flow rate with appropriate reinforcement.

The mesh and basket should be an integral unit, with the mesh fastened to the basket both at the top and the bottom to prevent any debris from bypassing the unit. In general, the open area perforation ratio should be about 4:1 to avoid excess pressure drop through the unit. A smaller ratio will require frequent cleaning.

Additional strainer basket area can be obtained by using a pleated basket. If finer filtration is required, a mesh liner can be added inside the basket. If the size particle to be removed is known, the perforations should be slightly smaller. Fluid streams may contain iron or steel particles small enough to pass through the finer screens.

If this is a problem, a strong magnet capable of lifting several times its own weight should be suspended in the basket. The magnet must be installed so that water passes over it. This magnet should be encased in an inert material to prevent corrosion

The baskets can’t withstand the same pressure as the body. A particular phenomenon called runaway buildup is possible, in which the dirt builds up and plugs the mesh or perforations, thereby reducing the free area.

The pressure in the sieve increases slowly at first but then increases more rapidly with time. The velocity and pressure of the water inside the basket intensify with speed, which causes the resulting flow to stop or to be reduced to a trickle. This full-line pressure can burst the basket.

STRAINER COVERS

The cover is the part of the device that should be opened to clean the basket. The most common type is bolted, the bolts must be loosened and removed to bring access to the basket. This type of cover is the strongest and should be used for high-pressure applications.

Another type of cover is the clamping yoke, in which threaded, tee-shaped handles are used to connect the cover to the body. Often, the cover is attached to the body with a hinge mechanism, making it easy to remove. This type of cover is more expensive than the standard one.

Another type of strainer is the automatic type (which does not require manual cleaning). A rotating, circular screen is used as the basket. The water inlet goes into the basket. A rotating backwash inlet inside the basket uses the differential pressure between the atmosphere and line pressure to produce a localized reverse flow across only a portion of the basket, thereby allowing continuous cleaning.

This type of strainer is appropriate for large consumers of water such as raw water inlets from rivers and lakes used for cooling and process. Automatic pipe strainers are available to 60-in (150-mm) size.