When working with specialized machinery such as vacuum trucks, it only makes sense that in order to properly use and care for such equipment, it is essential to understand how it all operates. There is a lot more to the functioning of one of these vehicles than simply turning on the pumps and using the hoses.
The truth of the matter is that many of the workers who daily use the equipment do not actually understand at all how all of the various parts that make up a vacuum truck work together to complete the job. Such lack of understanding is not only detrimental to the machinery itself; it is downright unsafe.
Since vacuum suction is how these vehicles are able to perform the work to be done, it would be a good idea to understand how vacuums work, to begin with. With this specific mechanism, it all begins with the pump that has fans inside spinning at high speeds; this action creates pressure that draws material into the attached hoses to be taken into the truck’s tank.
The pump is powered by the power takeoff (PTO) on the truck’s transmission, which gets its power from the vehicle’s transmission. In neutral gear, the PTO switches the power from the transmission to the PTO, providing power to only one mechanism at a time.
It is the speed at which the transmission turns that determines how strong the pressure and suction will be, at least as far as that pump’s capabilities. The only other part in the equation is the inside rotating fans that need to be kept well oiled, either by an automatic built-in oiling device or an attached, separate oil tank.
In order for the PTO to be powered by the rpm’s of the turning transmission, there must be a gearbox between the two. This provides for the adjustment of the transmission speed from outside of the truck, which is necessary because it is the number of rpm’s that determine how fast a pump can run and how strong the suction will be. This gearbox also converts the speed of the transmission to match the speed needed by the pump as the setting is not usually at a 1:1 ratio.
Once connected, the gearbox and PTO convert transmission energy into suction power. Many arrangements may also include a Woods coupler between the PTO and the pump, which protects the latter from damage that could occur from rough starts when the PTO is first connected and an attempt is made to turn the pump.
When vacuum trucks are used to suction either wet or dry material, the high airflow created by the pumps draws the material into the hose nozzle and then the hose, where it is deposited into the truck’s tank. The air drawn into the tank is then forced back out of the tank, into the pump and out the other side into the air, creating a flow of continuous suction.
The important thing to remember is that air being forced out of the tank will pass through a number of filters to catch solid and liquid debris before it can enter the pump and cause damage. Such filters do clog and impede the airflow, which decreases or even stops the ability to suction at all.
The above illustrates the simplicity of the vacuum pumping process and how few parts actually operate the system. Such simplicity makes vacuum trucks easy to repair for the most part; it also allows for the system to be checked on site in order to determine the location of a problem. Most importantly, it is vital to understand how the equipment needs to be operated to prevent damage to any vehicle parts and to avoid accidents. How a vacuum system operates really isn’t magic at all!