A vacuum truck works by first creating a vacuum in the tank. This is done by engaging a vacuum pump
which pulls air through the final filter and then the secondary and primary shut-off’s. A vacuum pump
uses rotary veins that rub against the pump case itself to create air flow in or out of the tank by way of
centrifugal force. There are at least six or more of these veins in each pump depending on the model
and they’re made of a Kevlar-type material. The final filter is designed to not allow passage of foreign
material into the pump via a mesh screen. Without this filter, the pump veins would get destroyed by
debris. The primary and secondary shut-off’s serve as safeguards to ensure that you do not overfill your
tank. They are comprised of a rubber seat and a stainless steel ball enclosed in a cage. The secondary
shut-off should be drained after each time you unload the tank as it also functions as a moisture trap.
The most common platform on vacuum trucks used for small applications is a pump and motor
combination. It has a vacuum pump and self-contained motor that runs the pump. Others use a P.T.O.
or “Power Take Off” that is the component that distributes power to the pump from the transmission
upon which it is mounted. A coupling and sleeve system protects the transmission if the vacuum pump
fails. Also, there is a vacuum relief valve and a pressure relief valve that protect the vacuum tank from
too much vacuum or pressure.
Vacuum pumps are rated based on how much air it moves through the pump measured in cubic feet
per minute (CFM). Check the owner’s manual to find out exactly how many repetitions per minute your
vacuum pump should be set to run at but most range between 1,100 and 1,300 RPM’s. There are fan-
cooled vacuum pumps but, in my opinion, liquid-cooled ones are the better choice for most applications
as it seems they operate more efficiently. Again, in the owner’s manual, the manufacturer will list
specifically which pump oil you should use. It will also tell you what flushing fluid to use and how often.
Flushing fluid ensures your pump’s performance by removing and preventing deposits that can form
on the pump veins and case. If not done regularly, the pump’s performance will decrease significantly.
Vacuum pumps come equipped with an oil catch muffler designed to capture used oil that gets expelled
from the pump and to reduce noise. It is not unusual to see smoke coming from the muffler at times
because it catches about ninety-five percent of the oil discharged but not all of it. This should be
emptied daily.
Every manufacturer has individual and specific recommendations pertaining to pump size relative to
tank size. The tank size is typically determined by the truck’s gross vehicle weight (GVW). Evaluate the
area that you intend to service along with the capital available for the purchase in order to know what
size trucks, tanks, and pumps will be best for your business.
