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Hydraulic Power Deployment
Published in Qin Zhang, Basics of Hydraulic Systems, 2019
In many applications, it is required that the HST be able to reverse operating directions. To offer this capability, a bidirectional HST often uses an integrated load-releasing and charging circuit to prevent either excessive pressure from being built up in the supply line due to overload or cavitation in the inlet line because of insufficient flow. As illustrated in Figure 4.30, integrated circuits commonly consist of two pairs of check valves, one for releasing high pressure from the supply line and the other for recharging additional flow to the inlet line as needed. The released flow can be either recharged to the inlet line or dumped back to the tank according to the operating condition. For design simplicity, in many cases, a shuttle valve instead of a pair of check valves is used to release excessive high pressure. This shuttle valve is always shifted by high-pressure fluid to connect the high-pressure line to the cross-relief valve to offer the excessive high-pressure releasing function. Similar to the unidirectional HST, a charge pump is also commonly designed in an integrated releasing–recharging circuit to provide the two main functions of preventing cavitation in the main pump by refilling the fluid lost in the closed circuit and providing pressurized fluid for actuating variable-displacement control on either or both the pump and motor in an HST.
Programmable Logic Control Systems
Published in L. Ashok Kumar, M. Senthilkumar, Automation in Textile Machinery, 2018
L. Ashok Kumar, M. Senthilkumar
Some symbols for pneumatic systems are shown in Figure 3.31. The flow control valve is used to restrict the flow, typically to slow motions. The shuttle valve allows flow in one direction, but blocks it in the other. The receiver tank allows pressurized air to be accumulated. The dryer and filter help remove dust and moisture from the air, prolonging the life of the valves and cylinders.
An efficient, compact and low-cost Dual Cylinder Hydrostatic Actuator (DCHA)
Published in International Journal of Fluid Power, 2018
The efficiency of the system while lowering in High Force mode can be further improved with the addition of an additional solenoid valve, as shown in Figure 18. In HF mode, when the cylinder is retracting, approximately twice as much fluid exits the cylinders as enters, with the excess flow venting to the charge system. Without this solenoid valve, this occurs when PB exceeds the workport relief valve setpoint pressure, causing the energy in a large volume of pressurised fluid to be lost. With the addition of a parallel solenoid valve, this fluid can be vented at low pressure, reducing the energy loss, as shown in Figure 19. As this limits the maximum rod end pressure, the maximum negative force is limited in High Force mode; however, there is no difference in the maximum negative force between HE and HF mode, so HE mode can be used in this situation. An efficiency increase can also be achieved for a similar reason by bypassing the check valve when extending, although the pressure drop is much smaller, so the magnitude of this effect is smaller. This valve provides a similar functionality as the pilot-operated check or shuttle valve seen in other implementations, but does not contribute to instability issues seen with these valves.