6. Hydraulic pet cocks are available for replacement of the hoist cylinder air bleeder valve, however, do not trust just any
old pet cock. Radiator and air brake type, low pressure pet cocks can deadline your truck with a leak or could be
dangerous with a blow out. A hydraulic pet cock, having a minimum rated capacity of 2000 psi and featuring o-ring seals
and a 90 degree twist handle-with open and closed dentent positions, would be acceptable. The run-of-the-mill brass pet
cock bodies usually withstand 3000 psi pressures, however, leather seals are questionable and quality control of the
inexpensive pet cocks are uncertain. These pet cocks are not designed for high pressure hydraulic use.
7. The CCE-IHC Dump Truck is equipped with a hydraulic system having a 1200 psi relief valve setting. Spike hydraulic
pressures may reach about 2000 psi. Ignoring friction in the system, hoisting the body should require about 90 psi,
empty, and should require about 600 psi, loaded. Near the 50 degree maximum body hoist angle, the hoist control safety
cable should pull back the in-cab hoist control from "HOIST" to "HOLD" control valve position. As a result, the hoist
pressure should normally not exceed the pressure of 600 to 900 psi needed to hoist the load. Before the hoist reaches
the limit of travel and causes the oil to spill over the relief valve, relieving pressure, the properly adjust hoist control cable
should automatically stop further hoisting of the body. With everything normal and correctly adjusted there is a low risk
that the dump truck hydraulic system would damage the radiator or air brake system pet cocks, however, with some slight
misalignment or unusual loadings, a 2000 psi peak hydraulic pressure could occur and put your truck out of commission.
178
