|The purpose of the valves in a reciprocating
to let air in and out of the cylinder
during the compression
process. These valves are considered
automatic because they
are operated by the difference in pressure
valves. The key to long valve life
is to have positive
action of the sealing components with
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.
compressor is running at 500 rpm for 24
hours a day, the
valves will open and close 720,000 times
Valves have to perform with minimum resistance
or power will
be wasted and components will wear at
All of this is why valve maintenance should
be considered a
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
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
specifications. The internal valve
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,
in-house or at an outside vendor, should
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
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
It is possible to run reciprocating compressors
out of tolerance and it happens more than
you think. It is
just not the best plan for getting the
most from your
b) Making the switch to a synthetic
If you operate a lubricated style of compressor,
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
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
The combination of these factors make it
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,
formulated in the piping and found its
way into every
filter, regulator, etc. downstream from
This is a short term maintenance concern
that should be
explained to everyone involved with the
Synthetic lubricants cost more than petroleum
oils but you
get a lot more for your money.
c) Cleaning up the oil going to your
If you operate a lubricated style of compressor,
want to avoid supplying dirty oil to the
lubricator boxes used on most industrial
hold between ½ gallon and 2 gallons.
This small reservoir
must be checked and filled often.
The process of refilling the box often
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
accumulates particles of dust between
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
There are a few things you can do to improve
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
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
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
reservoir systems are available from Direct
Supply. You can
reach them at email@example.com
if you have any
questions or would like a quotation.
d) An easy way to monitor your inlet
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.
compressor did not come with such a device,
you can make a
simple modification and take the guesswork
out of filter
Compressor operators have many options
available to monitor
inlet filter efficiency. There are
2 very simple types of
indicators being used by industrial customers.
both easily installed into the inlet piping,
about 24? about
the connection to the compressor inlet
The first type is called a manometer which
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
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
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
to avoid condensation forming in the cylinders.
inspection rarely detects this unless
there has been
significant liquids and a chance for rust
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
Do you operate valves with straight ports,
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
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.