Filtration

FILTERS

The purpose of FILTERS ---

according to general definition: Is to keep contamination transported in the air and oil out of the compressors.

Compressors together with gearboxes, fluid-power system (hydraulic & pneumatic), internal combustion engines and industrial machinery have a common problem:

"Wherever moving parts contact or mesh with one another, FRICTION results."

This friction has to be reduced. to this end, a suitable, mineral or synthetic oil, is used to provide a sliding film between the moving or rotating parts of the machines.

This is only possible if the lubricating oil stay clean and remain clean. If foreign particles, even if they are microscopic in size, are transported with it. Such particles can reach the moving or rotating parts inside the compressor in the form of sand or dust in the oil or air intake.

Whenever friction occurs, fine metallic abrasives are created, found it's way in the oil, creating even more metallic particles to get into the compressor oil or coolant. Critical areas within the compressors are the compressor case (housing), screw rotors, seals, bearings, gears, valves etc.

In addition, compression does not occur without leaving residues. If this is nor filtered out, the foreign particles acts as an abrassive mass, which can considerably accelerate wear on the moving parts.

Also, dirt particles when in excessively high concentrations though they are not as hard, can be dangerous for compressor. It can damage the compressor due to inadequate lubrication and cooling.

A well-maintained and effective oil filtration system along with good air filtering, is the best guarantee of long compressor life.

Main-flow filters and air inlet filters are usually designed for 25 micron particles filtration and 10 micron for bearings

Built-in Safety System

The minimum pressure valve (MPV) has a secondary purpose, that is, acting as a non-return valve when the compressor stops or off-load.

This is to prevent the line air pressure is not lost by reverse flow from the air system back to atmosphere via the compressor.

When the compressor stops, the intake valve is automatically closed, and the internal pressure within the compressor is gradually reduced or vent out to the air intake.

This is achieves by mechanically, hydraulically or electrical solenoid valve.

This is to prevent hydraulic locking and possible damage when the compressor restarted. The compressor will start with a light load and low starting current.

Safety Devices

HAT = Hight Air Temperature Switch = Trip at 110 degree C

Safety devices are install to protect the compressor against malfunction due to

high air oil temperature,

lack of oil,

lack of cooling air or water or

abnormal electrical supply.

Monitoring Devices

Monitoring devices are also installed, Certain design have more components and some with the minimum number.

Signals when filters are to be cleaned or replace,

Separator differential pressure,

minimum & maximum pressure,

oil & air end bearing temperature readings,

water separator conditions,

hour meter,

motor conditions to indicate maintenance frequency.

Compressors with constant running control, start-stop control, manual dual control, automatic dual control, lead-lag operation for multiple compressors application.

Run-on timers for keeping the compressors running to minimize condensation during short demand periods, run-on timers to shut down compressors when there is no demand for air, are offered by various manufacturers.

They are compact, free from vibration, and with low noise levels. The air delivered is cool, clean, and free from pressure pulsation, and in some cases air receiver is not necessary.

They can be mounted anywhere including immediate work areas.

Panels may be included to reduce noise level, panels for outdoor usage may also be order.

Positive Displacement Compressors-Operation

Operation

The lubricating-cooling system consist of oil filter, minimum pressure valve (MPV), a heat exchanger.

Thermovalve and in some designs (usually the bigger horsepower units), temperature control (regulating) valve is used to maintain a relatively constant temperature regardless of compressor load.

Oil Circulation

The use of Compressor lubrication is very important! and cannot be denial? Especially the grade and type of lubricant use.

Oil circulation is usually provided by the pressure-differential system. Circulation in the pressure-differential system is achieved by using higher-pressure air to generate the oil flow.

A preset minimum pressure valve (MPV), usually about 80 psi, allows the quick pressure build up in the oil sump before the MPV opens to discharge compressed air to the air system.

MPV

The pressure differential between the fully compressed air, and the pressure within the cell as it passes or rotates. The pressure differences thus created, caused the oil to be injected via orifices into all moving parts, including the rotor bearings located in the end covers of the stator..

Internal Valve position = = = = = Compressor at loading

In all and every cases, the compressed air pressure is relieved automatically from the discharge side of the compressor during shutdown. Therefore, with this design and operation, there will be oil presence in the compressed air.

It is not desirable to have oil in the compressed air, and it is necessary to remove the oil before it is send to the air system.

Oil Separation

Therefore; as air and oil mixture passes from the compression chamber, the oil, which is heavier, is mechanically separated by direction and velocity changes, or use of baffles, or of both, and allowed to drain back into the oil chamber or oil sump for recirculation.

Relatively clean air leaves the sump and enters the separator, where most of the remaining oil is removed by coalescence called air/oil separator/s. The coalescence (separating media) are ceramic tubes or combination of mesh & fibre glass (Boros Silicate).

The Scavenging Line

The separated oil (residue oil) drains from the coalescing media to collection well for subsequent return via a combination of orifice and check valve to the intake side of the compressor.

Oil Carryover

The amount of oil carried over is less than 5 to 1 ppm of air measured by weight. Air losses through the oil return (scavenging) line is controlled by an orifice. The resulting pressure drop through the separator should be approximately 1 to 3 psig, when new. Should change or replace the separator when the pressure difference is at or more than 15 psig.

Heat Exchanger

Air-cooled or water-cooled heat exchanger are used for the oil. The air-cooled heat exchanger is of radiator type, with a cooling fan to provide air circulation.

The water-cooled is shell & tube type, and need an external water circulation and cooling system.

Oil circulation at start-up

On start-up, oil bypass the heat exchanger (cooler) and circulates through the compressor and sump with cooling. This provide rapid oil supply & heating on start-up.