Forklift Charging Pump
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The technical document below describes the charging pump, its functions, and the essential valves.
Table of Content
- What is a charging pump?
- Important valves
- Charge pump suction filter
- Symptoms of a weak charge pump
What is a charging pump?
The hydraulic charge pump drives the hydrostatic pump loop via a fixed-displacement pump (typically a gear pump). The primary aim of the charge pump is to provide fluid to the system.
This bypassing causes less oil to exit the motor than the primary pump needs. Charge pumps provide make-up oil through a check valve, preventing pump cavitation. Charge pumps also provide oil for stroking the main pump by supplying it to spring-loaded cylinders.
Figure 1: Forklift Charging Pump
The function of a charging pump includes:
Closed-loop systems require that the case drain oil from the pumps and motors be added to the tank to prevent cavitation of the pump, a function that is controlled by the charge pump.
- Auxiliary Control Functions
It is possible to use charge pumps to provide enough power to operate remote hydraulic servo controls or hydraulic brakes.
Many hydrostatic transmission pumps include a filter in the charge pump inlet manifold that forces the oil through the filter before it reaches the main pump. Over time, all the drain oil in the circuit is cleaned by filtering.
- Maintains the back pressure
Having a constant inlet pressure is crucial to HST systems. Charge pumps maintain inlet pressure and can be customized to fit specific PSI levels and inlet pressure requirements, depending on your HST needs.
When the charge pump is idle, the relief valve allows the excess pump volume to return to the tank. Relief valves are usually mounted near or on charge pumps. It usually discharges into the pump case, returning to the tank via the main pump's case drain line.
The charge pump and low-pressure side of the loop are connected by make-up check valves that allow free flow. The opposite check valve prevents oil from moving from the high-pressure side to the low-pressure side. When the charge pump is removed, the check valves can be accessed.
Crossport relief valves regulate the maximum pressure in the system. During mechanical stalling, the relief valve on the high-pressure side of the loop would open and dump fluid back into the low-pressure side, protecting the motor. Depending on the system, pumps, hydraulic motors, or separate blocks may contain the valves.
Charge pump suction filter
Oil is cleaned through this filter before reaching the pump's suction port. Most of them are non-bypassing and are rated at 10-microns. A regular schedule should be followed for changing and cleaning the filter. If it becomes contaminated, the charge and main pump may cave.
Figure 2: Toyota Forklift Charging Pump
Symptoms of a weak charge pump
- No movement of the pump
- Controls show resistance
- Drive motors making a high-pitched squealing noise
- The hydraulic charge pump drives the hydrostatic pump loop via a fixed-displacement pump.
- The function of a charging pump includes replacing fluids, auxiliary control functions, filtration, and maintaining the back-pressure.
- A regular schedule should be followed for changing and cleaning the filter.
Lift parts warehouse has a wide selection of charging pumps, OEM, and aftermarket supplies. Finding a good quality forklift charging pump at a low cost is one of the things our team does.
You can learn more about the product here and contact us if you need help ensuring this is the proper application. Our suppliers are trusted and have been delivering quality products for many years.