One of our members described the hydraulic layout of a rear-mounted knuckle crane on a truck, which was giving trouble, as follows:

“The pump is a bent axis Muncie pump 20 GPM, 4300 PSI. The pressure line is 3/4″ hose and steel tube. The pump intake line is a 2″ suction hose from the tank located on the crane base to a 1-3/4″ steel pipe under the truck bed and back up to a 2″ hose between the steel pipe and pump. Total length of each line (pressure and intake) is 33 feet. The intake line also features one, 45-degree fitting and three long-radius, 90-degree bends.”

One of the great advantages of a hydraulic system is that components can be mounted with little regard to alignment, and within reason, proximity to other components with which they must connect.… continue reading »

The charge pump on a closed-circuit, hydrostatic transmission has a number of important functions. These include:

1. Replenish fluid lost from the transmission circuit due to volumetric inefficiency of the pump and motor.
2. Replace fluid purged from the circuit via the hot-oil flushing valve (where fitted).
3. Supply make-up fluid to compensate for load-induced oil compression and conductor (pipe/hose) expansion in the transmission circuit.
4. Provide a flow/pressure source for activation of pump and motor servo controls.
5. Provide a flow/pressure source for auxiliary functions such as parking brake release and pilot controls.
6. Maintain sufficient pressure on the low side of the transmission circuit for ‘hold down’ and hydrostatic lubrication of the pump/motor rotating group.… continue reading »

One of our members sent me this story from the coal face:

“I have a question about some trouble a hydraulic machine has been giving me at work. The pump set is designed with vane pumps located on top of the reservoir with suction strainers. The trouble is that at odd times a pump (any one of the three) will not prime up. Once primed, the machine runs OK. But from time to time after a break or lunch when they restart, a pump will not prime. Any thoughts will be appreciated.”

Ideally you would never have the pumps mounted on top of the reservoir (flooded inlet is best for all hydraulic pumps) or have suctions strainers installed.… continue reading »