filter location ?

Filters are best on the discharge side. Filters result in head loss and if placed on the suction side may cause loosing the NPSH available.

Circumstances may sometimes dictate a filter on the suction side. A flooded suction and proper NPSH calculations are then needed.

For example pumping from a shallow (dirty) river with a suction manifold grid covered with filter material.

Why do you require a filter on the suction side?

Filters, strainers and traps, are piping system components designed to help protect the system. They protect them from harmful solid or fluid impurities. Many problems that occur in a system are caused by impurities in the fluid.

STRAINERS.

Strainers are devices made of a single piece of wire mesh, or sheet metal with holes in it. They are designed to removed all the large solid particles from fluids. Most strainers are made of stainless steel or brass.

Strainers cannot remove the small particles like a filter, but they do offer less resistance to flow. They can be installed ahead of valves, pumps, regulators and traps. They are used in pipe lines carrying water, air, gas, steam, and most other fluids.

Many problems in hydraulic systems are caused by impurities (particles, of dirt and sand etc.) in the fluid. Impurities can cause the system to break down. It is less expensive to install a device to remove them, than have to repair some fault.

Strainers are installed on suction lines where the pressure is low. If there is a restriction in a pump suction line, it can stop the fluid getting into the pump.

Low pressure in the suction line can also cause cavitation. Cavitation is a condition where there is not enough fluid at the pump inlet to keep the pump body full. This causes vacuum cavities to form in the fluid stream. Cavitation can cause a mechanical breakdown.

Strainers are also used as screens to keep dirt out of reservoirs. This is common in hydraulic systems.

To help prevent dirt getting into the reservoir, always make sure the reservoir cap is replaced after filling.

There are three common types of strainer, they are as follows:

· Cone type. This is the most efficient type of strainer because of its large surface area.

· Disc type.

· Magnetic type. This type is very useful because 50% of all particles in fluids are ferrous.

Before any maintenance work is carried out on a strainer, always make sure that the line has been isolated, and that a work permit has been issued.

FILTERS.

Filters are made in various shapes and types. They are used to remove the smaller particles from the fluids. Filters are like strainers but can have several layers. They are made from cloth, metal, and glass fibres, metal powder, paper or glass.

The filter removes the particles by passing the fluid through the porous barriers. All filters change the direction of the fluid as it passes through it. This slows down the particles.

There are three common types of filter, they are:

· Edge, or full flow type. These consist of a series of discs with holes in their centres. The discs are separated by a small space.

· Cartridge type. These are similar to car filters.

· Filter bed. These consist of sand and gravel.

STEAM TRAPS.

Any steam piping system can contain a small amount of water in with the steam. This water must be removed from the steam line. Steam is often used to run a steam turbine. Any water in the steam lines feeding a steam turbine can damage the turbine vanes. Steam and hot water under pressure in piping systems are very dangerous. They can cause rust and corrosion. Steam traps are used to remove the water from the steam lines.

There are two general types of steam trap, they are:

· Thermostatic steam traps." They respond to temperature changes or drops in pressure.

· Mechanical steam traps. They respond to water level.

Types of steam.

· As water comes to the boil at 100°C (212°F), steam forms. Small particles of water are carried inside the steam. This is called wet steam, and is visible.

· If more heat is applied then all of the water will turn into what is called dry‑saturated steam. This kind of steam is invisible.

· If still more heat is applied then it will become what is called superheated steam, or dry steam.

If the pressure drops for some reason, boiling will occur at a lower temperature. Dry‑saturated steam could then become superheated steam.

If the pressure is increased, then the temperature that the water boils will be higher.