The hydraulic system
on your tow truck is designed to have an air vent so pressure cannot build
up in the hydraulic oil tank. The manufacturer usually installs a
vented cap on the tank filler tube. The hydraulic system needs a
vent because the oil level in the tank must be free to go up or down as
oil comes back from and goes out to the hydraulic cylinders when you
operate the tow truck bed. When someone defeats the vent, they
usually do so without intending so. The results can range from minor
loss of hydraulic oil to destruction of the hydraulic pump, reservoir and
hoses.
Last year, a car carrier was in
my shop for repair because the suction hose had blown off the hydraulic
pump and all the oil in the hydraulic system was lost. Pressure
inflated the steel hydraulic tank like a water balloon so its sides were
rounded instead of flat. Because the operator had continued to
operate the equipment even after becoming aware of the spreading lake of
oil under his truck, the pump completely burned out from running dry.
I looked closely at the tank and
noticed that someone had replaced the original vented filler cap with an
otherwise identical non-vented plumbing cap you can buy at any hardware
store. They had filled the tank with oil, installed their new
non-vented cap super-tight with a pipe wrench, and then operated the car
carrier.
What's a smart solution to this
problem? Drill a vent hole in the filler neck, not in the cap.
It doesn't cost you any more money or time to drill the hole in the filler
neck, which is a permanent part of the tank, rather than in the cap.
Making the vent in the neck will
positively determine the direction of overflow, rather than leaving the
direction up to the vagaries of cap tightening. By drilling your
vent hole pointing inward toward the truck, you can save friendly
bystanders a warm, high-pressure oil shower when someone's overfilled the
tank.
