REXRTOH A4VG series 40 axial piston variable displacement pump application guide

Hydraulic oil, working conditions, and filtration requirements

1. Hydraulic oil selection

Recommend using HLP mineral oil that complies with DIN 51524. The selection of oil should ensure that the operating viscosity is within the optimal range (ν _opt=36... 16 mm ²/s) at the system operating temperature to achieve maximum efficiency and component life. Bosch Rexroth's "Fluid Rating" system (technical data 90235/90245) provides important reference for oil product selection.

2. Range of work pressure

Working port A/B: rated pressure 450 bar (maximum design pressure), peak pressure 500 bar (single operation cycle ≤ 10s, total time ≤ 300h).

Oil replenishment pressure: rated at 25 bar, maximum at 40 bar.

Shell pressure (T port): It is necessary to strictly follow the pressure difference (shell environment) - speed curve to prevent damage to the shaft seal.

Pressure change rate: maximum allowable 9000 bar/s.

3. Filtering requirements

To achieve and maintain an oil cleanliness level not lower than ISO 4406 20/18/15 (19/17/14 required for short-term high-temperature operation), an efficient filtration system must be configured. Fine filtration is the key to extending the service life of pumps. For the oil replenishment circuit, various options are provided, including oil suction filters, oil pressure pipeline filters, and accessory filters directly installed on the pump. Special note: For versions with accessory filters (F, B type), a minimum conductivity of 300 pS/m is required for hydraulic oil to prevent static accumulation in the filter element.

Key functions and safety components

1. High pressure safety valve

Two integrated high-pressure safety valves (one at port A and one at port B) are the primary overload protection for the system. They set the pressure difference (Δ p_HD) between the working pressure and the refueling pressure, rather than the absolute pressure. For example, if the working pressure is designed to be 450 bar, the oil replenishment pressure is 20 bar, and a safety margin of 30 bar is considered, then Δ p_HD should be set to 460 bar. At this time, the absolute opening pressure of the safety valve is about 480 bar. When placing an order, it is necessary to clearly specify the Δ p_HD setting value.

2. Neutral valve

An electromagnetic switch valve is used to force the pump back to zero position and unload the variable cylinder when it loses power, ensuring that the drive system is "disengaged", enhancing safety, and accurately adjusting the return to zero time.

3. Mechanical travel limiter

By using two internally adjustable limit screws, the maximum displacement of the pump can be mechanically and continuously reduced, regardless of the control method used, providing the possibility of achieving power limitation or special function curves.

4. Swing angle sensor

A sensor based on the Hall effect can detect the angle of the inclined plate (i.e. displacement) in real time and output an analog signal of 0-5V (or 1-4V) for display or closed-loop control.

Installation Planning and Application Guidelines

1. Installation position and oil injection exhaust

It is recommended to install the pump under the fuel tank (with the pump located below the lowest liquid level in the tank). If it is necessary to install on top of the fuel tank, the suction height must be strictly controlled (hs_max ≤ 800 mm), and the absolute pressure at the suction port S must not be lower than 0.8 bar (not lower than 0.5 bar during cold start). The pump must be adequately oiled and vented before installation or at a specific location (such as the drive shaft level), with particular attention paid to the venting of the variable cylinder (via X1/X2 or X3/X4) and the housing (via the R vent) to prevent dry friction and cavitation. Different installation positions can affect the control characteristics, and gravity, self weight, and shell pressure may cause slight deviations in the control curve.

2. Application of combination pump

Through through drive, two A4VG pumps can be connected in series to form a combination pump, providing independent circuits for different actuators. When placing an order, the complete order models of the two pumps should be connected with a "+" sign. Installing flanges with four holes is more stable. It is necessary to verify the transmission torque of the through drive shaft to ensure that the total torque of the second pump and its driving load does not exceed the allowable value.

3. Core considerations for project planning

Professional personnel: The planning, installation, and debugging of the system must be carried out by qualified professionals.

Safety function: The pressure cutoff function is not a safety device to prevent pressure overload. The system must be equipped with a safety valve (such as a high-pressure safety valve).

Dynamic power flow: When the pump operates as a motor under braking conditions, its displacement should not exceed 95% of the maximum displacement.

Peak pressure: Transient pressure peaks may occur in applications, and must be considered when selecting measuring instruments and pipe fittings.