Exhaust filters are often used on oil sealed rotary vane
vacuum pumps. The main
reason to use an exhaust filter is to eliminate or minimize oil mist
that can often be a byproduct of the vacuum pumps operation.
Oil mist is often generated by vacuum pumps for a variety
of reasons. The most
prevalent and common cause is operating the vacuum pump at
"high" pressures. Generally
speaking operating pressures above 1 Torr or 1000 micron can cause oil
mist to be apparent. Oil
mist creation is not unusual and "No the pump isn't on fire."
The most common cause is operating the pump by pumping against an
"open" or leaky system. The
pump then has very high gas flows going through it, and in the process
will atomize oil molecules (aerosol) and they will then attempt to exit
the pump and baring no filter media to prevent this, they will.
An exhaust filter or "oil mist eliminator" is a
more advanced filter usually containing a replaceable element that will
stop oil mist on a molecular basis or at least make a good effort at it.
Exhaust (oil mist) discharge can be cut significantly by adding one of
these filter items to your vacuum pump.
Not only does it keep the oil mist out of your workspace; it also
will keep the pump oil in the pump where it belongs.
There are two basic types and numerous variations in
these two categories. The
first is a standard exhaust filter; generally coalescing, that will trap
most of the oil mist, keep the oil in the pump and exhaust into the
workplace. Coalescing means
that the oil drains back into the pump after it condenses on the insides
of the filter element itself. The
second type of exhaust filter does the same as the first, but also
includes an exhaust port from the exhaust filter.
We call this a capture filter. With this filter a hose can be
hooked up to the filters exhaust port and any oil mist that gets by the
element can be directed via hose connection to a hood to remove from the
HyVac vacuum filter elements have been designed to
99.999% DOP efficiency on .2- .3 micron particles. They are rated at 5 parts per million at 60 Torr maximum
Oil mist filters are designed for oil mist.
These are pretty large molecules.
If you are dealing with volatile solvents or other types of work
place unfriendly items, then the second type of exhaust filter is the
filter for you. These types
of filters usually entail a little more installation cost due to need to
run hoses from pump exhaust to the hood but because they present a
closed loop to the hood for exhaust the user is assured a clean
All of the exhaust filters from HyVac are very easy to
install and either thread into the exhaust port of the pump or can be
clamped on in some relatively simple manner.
Filters will require changing from time to time and the
frequency depends on the amount of use the filter element in the filter
gets. A simple maintenance
program can be put in place once the frequency of actual changes needed
becomes apparent. If a
filter is allowed to operate after being all clogged up over time, then
back pressure may start to develop in your pump and may put undo
pressure on the shaft seals or other exit ports from the pump itself.
The motor will also tend to work harder in this situation, so it
is important to replace the element every 6 months or so.
Again it really depends on the amount of use the system gets.
Filter change out generally should occur when there is a pressure
differential of 2.5 psid across the filter.
Do I really need this thing? Depending on what you are pumping out of your system a good
exhaust filter, with a port to a hood may be a prudent investment.
Your pump has less of a chance of running out of oil with this
type of item in place. There
is less exposure for local personnel to the exhaust by products and
vapor streams from the pump. It is feasible to port the exhaust directly
to a hood, but then monitoring of the pumps oil level should be made a
routine preventative maintenance practice.
Take care to avoid any low spots in the exhaust line as oil may
collect there and again cause back pressure during operation.
Applications that use exhaust filters with oil sealed pumps.
removal for pressure unloading vents on piston compressors
application requiring low delta p coalescing of large air volumes
Exhaust Oil Mist
oil fog, mist, or smoke from exhaust on oil flooded vacuum pumps
vacuum pumping systems
Vacuum Processes Medical