Compressor valves serves as check valves for the inlet and
discharge passages of the cylinder and will open and close
once for every revolution of the crankshaft.  If the
compressor is running at 500 rpm for 24 hours a day, the
valves will open and close 720,000 times every day!

Valves have to perform with minimum resistance or power will
be wasted and components will wear at accelerated rates.
All of this is why valve maintenance should be considered a
top priority.

Time and effort spent on improving valve service life will
reduce the costs associated with downtime such as loss
production and compressor rental.  Longer service life means
you will not have to buy replacement parts as often.  And if
done correctly, you can practically eliminate the need to
replace the expensive valve bodies.

The following are some tips and suggestions for improving
valve service life.  These ideas are from mechanics with
experience dealing with compressor maintenance.
 

a)  Internal Valve Specifications

The starting point of valve maintenance is to make sure that
all existing valves are operating within original
specifications.  The internal valve dimensions and
tolerances establish the lift and flow area of the valve.
These, when maintained, make it possible for the compressor
to perform according to design standards.

The people responsible for your valve maintenance, either
in-house or at an outside vendor, should have a
specification sheet for each valve.  If you do not have
internal dimensions and tolerances for your valves, use your
influence with the manufacturer and persuade them to furnish
this information.  Remember, tolerances are as important as
the dimensions which means copying the dimensions off an
existing valve will not tell the whole story.

The nature of a reciprocating compressor can lull you into a
false sense of security by functioning with valves out of
tolerance.  The reality is that the components are slowly
building to failure and downtime with an unknown degree of
severity.

It is possible to run reciprocating compressors with valves
out of tolerance and it happens more than you think.  It is
just not the best plan for getting the most from your
compressor.
 

b)  Making the switch to a synthetic lubricant.

If you operate a lubricated style of compressor, you should
consider upgrading the cylinder lubricant from petroleum oil
to a diester based synthetic.  This move has proven very
effective at reducing valve maintenance.

The diester lubricant eliminates the carbon and varnish
build up on the wear parts, especially the valves.  In
addition, this type of oil is specially blended to provide
stabile viscosity, resist oxidation and reduce friction.

The combination of these factors make it possible to
increase valve service life.  The diester lubricant will
also provide greater safety from the hazards of flash fires
in the discharge piping.

There are many advantages but you should be aware that a
change to synthetic might increase your maintenance work in
the short term.  This is because the solvent additives in
synthetics are cleaning agents.  The oil carryover will
begin to clean the years of petroleum oil deposits in your
compressed air system piping.

Some customers have reported that a dark, sticky residue
formulated in the piping and found its way into every
filter, regulator, etc. downstream from the compressor.
This is a short term maintenance concern that should be
explained to everyone involved with the air system.

Synthetic lubricants cost more than petroleum oils but you
get a lot more for your money.
 

c)  Cleaning up the oil going to your cylinders.

If you operate a lubricated style of compressor, you will
want to avoid supplying dirty oil to the cylinders.  The
lubricator boxes used on most industrial compressors will
hold between ½ gallon and 2 gallons.  This small reservoir
must be checked and filled often.

The process of refilling the box often leaves the
opportunity for particles to find their way into the
lubrication.  It is common, for instance, to find the fill
cover was left off after the last refilling or has been lost
altogether.  Also, the fill process is usually to pump oil
from a 55 gallon barrel into a small container which
accumulates particles of dust between uses.

The end result is an accumulation of sludge at the bottom of
the lubricator box.  This is agitated by the lube box cam
shaft and leads to dirty oil being injected into the
cylinders.

There are a few things you can do to improve this situation.
The obvious strategy is to clean up the process of filling
the lubricator and to make sure all lube boxes are cleaned
out on a regular basis.

However, it might be easier to eliminate some of the
maintenance rather than add more to your crowded work
schedule.  You can accomplish this by installing an
auxiliary lube reservoir.

These extra reservoirs are available in 5, 15, 30 and 55
gallon sizes and connect directly to your existing box.
They are easy to install and reasonably priced from about
$350.00 US for the 5 gallon unit to just under $500.00 US
for the 55 gallon unit.

This type of auxiliary lube supply system is furnished with
a stand, gauge, float valve, hose kit and a tank with a
sight to monitor the oil supply.  The float valve mounts to
an open port on the lubricator.  It automates the gravity
flow of oil from the tank.

Another idea is to install individual filters on each line
carrying lubrication to the cylinders.  There is a sintered
bronze filter that sells for about $60.00 US that has been
successfully used in this application for many years.

The lube line filters and the above mentioned auxiliary lube
reservoir systems are available from Direct Supply.  You can
reach them at lube@compressorwise.com if you have any
questions or would like a quotation.
 

d)  An easy way to monitor your inlet air filter.

Dirt and other airborne particles will cause damage and
reduce valve life.  The solution is to furnish the
compressor with clean inlet air and to stay on top of filter
maintenance.  This is ?easier said than done?, especially
for the older stationary compressors in today?s world of
smaller maintenance departments.

The new compressors being sold today are supplied with a
variety of devices to monitor filter life.  If your
compressor did not come with such a device, you can make a
simple modification and take the guesswork out of filter
maintenance.

Compressor operators have many options available to monitor
inlet filter efficiency.  There are 2 very simple types of
indicators being used by industrial customers.  They are
both easily installed into the inlet piping, about 24? about
the connection to the compressor inlet flange.

The first type is called a manometer which monitors
differential pressure across the filter.  A manometer should
show between 0 and 1 psi with a new filter.  A rule of thumb
is to replace the filter when it reads 10 psi.

You can buy manometers, for under $60.00 US, from any
industrial supply company, such as Grainger.  If you call
them at 1-800-487-3279 or at 1-847-535-1000, they can put
you in touch with their nearest office.  They can also help
you pick the right product for your application.

Another product that can be used to monitor inlet filters is
called a restriction indicator.  This measures the
restriction on the filter and provides a signal to indicate
the filter condition.  The indicator is green when the
filter is new or still has service life.  However, if the
indicator turns red, the filter is contaminated and needs to
be replaced.

Restriction indicators are available for under $40.00 US
from several sources.  One manufacturer is Donaldson Company
in Minneapolis, MN.  You can reach them at 1-800-374-1374 or
1-612-887-3131 and they will put you in touch with the
distributor in your area.  They can also help you size an
indicator for your specific application.
 

e)  Other tips

Monitor the temperature of the water cooling the cylinders
to avoid condensation forming in the cylinders.  A visual
inspection rarely detects this unless there has been
significant liquids and a chance for rust to form.

The condensate will damage the valve parts.  The problem is
worse in lubricated cylinders because the condensate will
wash away the oil.

The temperature setting may need to be adjusted for the
seasons or to compensate for deposits formed inside the
cylinder water jackets.  Check your owner?s manual for their
recommended water outlet temperature.  A rule of thumb is to
keep this temperature between 100 degrees F and 130 degrees
F.

Do you operate valves with straight ports, including strip,
feather and channel valves?  If so, they need to be
installed with the ports parallel to the piston rod.  This
lets the valve open evenly and avoids the erratic wear
caused by the rolling action of the internal sealing parts.

The final point is to make sure you can trust your supplier
of valve parts.  The best choice is any company, not
necessarily the OEM, that has control of the manufacturing
and quality control processes.

Ask for a tour of their manufacturing plant or to see their
quality control manual.  Spending the time to find a company
committed to providing high quality valve parts can have a
dramatic impact on your maintenance program.