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Choosing a
Compressor |
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INTRODUCTION |
There are many different types of air compressors.
An air compressor basically compresses atmospheric air to a given pressure,
the air is usually stored in a pressurised vessel, the air receiver, as the
air expands it creates volume and speed which can be used to atomise paint
or power air tools.
For spraying the choice of compressor will depend on the air
consumption and pressure requirement of the Spray Gun, and the number of
spray guns used.
For the hobbyist a complete
spray system can be purchased including the spray gun, hose complete with
connectors and the air compressor at economical prices
(Compressor
Starter Kits).
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SPRAY
GUNS |
When selecting a
spray gun separately, it will be neccessary to check the average air
consumption in CFM (cubic feet per minute) or L/min and working pressure in
either Bar or PSI (pounds per square inch). A compressor can then be
purchased ensuring the FAD (free air delivery) of the unit and the pressure
is equal to or more than the air consumption of the gun, usually suction
spray guns need more air than gravity ones
Choosing the
right compressor for your needs and then properly setting up the system is
vital. If the compressor is too small the type of gun and quality of finish
can be affected. If the compressor is too large then unnecessary expense
will be incurred.
Using
compressed air for spray painting gives greater versatility (read
more...) and the extra benefit of having the
ability to operate other pneumatic equipment such as tyre inflators,
chipping hammers, air blow gun, impact wrenches, ratchet wrenches, etc.
The first factor to choosing a compressor is which type to purchase.
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Gravity Spray Gun |
Suction Spray Gun |
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COMPRESSOR TYPES |
The initial choice is between a
Direct Drive Compressor (mainly for hobby & less demanding work) and a
Belt Driven Compressor (more for workshop use).
Direct Drive compressors are of a co-axial design (motor directly coupled to
the pump unit), are normally single stage and therefore the atmospheric air
is compressed once. These units are inexpensive to buy and operate
efficiently at lower pressures.
Belt Driven compressors operate via belts and pulleys and can be single or
two-stage which will produce compressed air without working as hard as a
Direct Driven compressor. These units are more efficient, run cooler and
deliver a greater amount of air for the power consumed.
Belt Driven compressors are usually lubricated whereas the Direct Drive
models can be both lubricated and oil free. Oil free units are very popular
with the keen DIY enthusiast as these units are low maintenance and can be
transported easily and cleanly (no oil spills), they also offer less
contamination of the paint, when this is atomised. |
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Direct Drive |
Belt Driven |
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COMPRESSOR SIZE |
Fortunately it is easy to size a compressor since they are
all rated according to the air delivered (cfm or litres per minute). As a
guideline a 2HP compressor will deliver about 7 cfm and a 3HP compressor
will delivery around 10.5 cfm FAD.
When choosing a compressor it is important to calculate the amount of air
required. A spray gun that requires 7cfm average air consumption will
require a compressor of approx 2HP.
Another issue to look out for when selecting a compressor is the
application. For intermittent use, for example for spraying a garden fence
or kitchen cupboard a small Direct Drive compressor will be more than
adequate. A project that requires a more sophisticated spray gun and heavy
duty (many hours of use over several days) will require a compressor
producing much greater CFM normally a Belt Driven compressor of 3HP or
above.
Note:
HVLP Spray Guns require a lot of air, always check the air consumption |
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PORTABLE OR STATIONARY |
Most portable units are usually mounted on
either a 25 or
50 litre tank/receiver, they come complete with regulator, outlet coupling,
etc. they are usually
below 3HP and
are usually Direct Driven, Portable Belt Driven models are available
with a 50 or 60 Lt air receiver.
Static units are usually designed to be wired in and installed to a pipe
work system they usually start from 3HP and the tank/receiver size can range
from 100 litres to 272 litres,
the regulator and other accessories need to
be purchased separately.
It is also essential that the “portability” of the compressor
be taken into account. If the unit is to be used primarily for
spraying garden fences, inflating car tyres, infrequent use of ratchet
wrenches then a portable unit (wheels and handles) should be selected.
There would be no obvious reason why a large static unit would be selected
unless extra expense is to be spent on hoses and hose connections. |
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COMPRESSOR MAINTENANCE |
The life and efficiency of the compressor will depend on the
level of maintenance that is provided. When selecting the compressor great
efforts have been made to ensure the system is correct and the compressor is
not being worked over and above the design capacity. However, to ensure the
efficiency several simply maintenance tasks need to be done:
Draining the air receiver: – water collects at the
bottom of the tank/receiver during the compression stage and the amount can
depend on the climate. This can be done manually by opening the drain valve
located at the bottom of the receiver.
It is important that regular checks are made to ensure that
this apparatus is functioning correctly:
Lubrication: – it is important that the oil level is
checked regularly and “topping up” undertaken when necessary.
Filtration: – intake filters need to be changed
annually or when they become too dirty.
Service: – an annual service is advisable especially
on the larger units. Valve plates, gaskets and Non Return Valves (NRV) can
be checked and replaced, belt(s) for belt driven models to be tensioned or
replaced. Service work should be done by an approved engineer.
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USE YOUR SPRAY GUN FOR: TIME SAVING – VERSATILITY – QUALITY FINISH – EASE OF
LEARNING - |
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