QUESTION:
I crawled under my truck last week and there was a big steel box that looked like a transmission. I wasn’t sure what it was but it was connected to my pump. So I asked a friend who would know to explain this “transmission” next to my drive transmission. He said it was my gearbox. He explained it but I’ll bet there’s more than one pumper who doesn’t know what the gearbox is or does.
Jeff Radcliff
Sarasota, Fla.
ANSWER:
Unless something goes wrong, you never worry about the gearbox, and you’re right. It is likely that many pumpers don’t have a handle on what it is and what it does. So let’s start at the transmission. From the transmission, the truck is put in gear, moves forward and backward. No mystery there.
But, to run the pump without an auxiliary engine, we need to borrow some power from somewhere. So we hook a power take-off (PTO) to the PTO port on the transmission. The power from the PTO is transferred to the gearbox before running to the vacuum pump to crank up some vacuum.
THE RIGHT RPM
The question then becomes, why use a gearbox? Why not just run the power from the PTO over to the pump and get the show on the road? Everything on a truck runs at certain speed and transmissions give the power to the PTO at a certain rpm. Transmissions vary the rpm depending on the truck. What we’re trying to do with the gearbox is make sure that we end up with the right amount of power at the pump to give us somewhere around 1,100 rpm on the rotor.
When checking the rpm of the PTO, for example, we might be coming out with 550 to 600 rpm. In this case, running it directly to the pump through a 1:1 gearbox means the pump is going to spin at 550 to 600 rpm. This is too low for the pump and isn’t going to get much done and may possibly damage the pump.
The gearboxes are made in three basic sizes. There is the 1:1, where the power transferred is the same as the power coming out of the PTO. There is the 1.5:1 where the power is boosted 50 percent. In the above example, if the PTO is turning at 600 rpm, the gearbox transfers power upward to 900 rpm. For this example, we still don’t have enough power to properly power the pump. The third size, and the proper one in this case, is the 2:1 gearbox. This doubles the rpm coming out of the PTO. Through the gear system in the gearbox (hence the name), the power is doubled and now there is 1,200 rpm running to the pump. This will work and is most likely within manufacturer’s specifications for the pump.
PROPER MAINTENANCE
Now that we have the gearbox in place and everything is working fine, what else might go wrong? Occasionally the driver will start the truck with the PTO engaged, which can put a jolt on the PTO, which carries through to the gearbox, and then to the pump. I’ve said it many times: The pump is your moneymaker. Protect it.
So how do we protect the pump from an absent-minded driver? Between the gearbox and pump we install a Woods coupler. The Woods coupler can best be described as two pieces of hard rubber encased in steel shell. This joins the two drivelines and in the case of sudden jolts, the coupler absorbs the shock, but will most likely be damaged.
When this happens, the pump is still in good shape. No harm done. But the Woods coupler needs to be replaced. Not a bad deal, you save a $2,000 pump but have to replace the $50 coupler. There are times when the Woods coupler, through aging or wear, will simply break down. Better the Woods coupler than your pump, the gearbox or the PTO.
The Gearbox is designed to provide optimum use of your pump and the Woods coupler is there to protect the system from expensive mishaps.
