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Pressure Control
Published in John S. Cundiff, Michael F. Kocher, Fluid Power Circuits and Controls, 2019
John S. Cundiff, Michael F. Kocher
A schematic of a direct-acting relief valve is shown in Figure 3.4. Valves like this are “poppet” valves, meaning that they have an element that moves (pops open) to open a single passageway for flow through the valve. Pressure acts on the annular area of the valve spool. The hydraulic force is given by
Hydraulic Power Distribution
Published in Qin Zhang, Basics of Hydraulic Systems, 2019
Direct-acting valves are generally used for small flow applications. This type of valve normally has negligible leakage below the cracking pressure and responds rapidly after surpassing the cracking pressure, which makes these types of valves ideal for relieving shock pressures. The rapid responding characteristics will also make the valve open or close quickly when the pressure exceeds or drops below the cracking pressure and results in a frequent alteration between opening and closing. This feature also makes this type of valve suitable for use as safeguard valves to prevent damage caused by high-pressure surges or to relieve pressure caused by thermal expansion. In addition, the differential between cracking and full-flow pressure on direct-acting poppet valves is normally high, which, together with the high frequency of open–close alterations, makes this type valve not recommended for precise pressure control.
Pneumatic components (1)
Published in Chris Stacey, Practical Pneumatics, 2012
Valves are of two main types: the poppet valve (Fig. 9.9) which seals on the face or faces of the internal moving part, and the spool valve (Fig. 9.10) which seals on the outside diameter of the moving sleeve called the spool. The majority of directional control valves, including all the larger sizes, are spool valves.
Dynamic characteristics evaluation of balance valve for seawater hydraulic variable ballast system considering the depth variation
Published in Ships and Offshore Structures, 2022
Zhenyao Wang, Yinshui Liu, Qian Cheng, Hao Pang, Yunxiang Ma, Shendan Zhao, Wei Wang, Defa Wu
SHVBS consists of many parts, such as a seawater pump, balance valve, stop valve, water tank, etc. The balance valve is arranged at the outlet of the seawater pump. The submersible is a closed environment, and the vibration caused by the pressure pulsation of the balance valve deteriorates the working environment of the submersible (Wu et al. 2017), especially for the manned submersible (Wang et al. 2020). And the outlet pressure of the seawater pump, the load of the motor, and the loss of energy are directly determined by the dynamic characteristics of the balance valve. So the dynamic characteristics of the balance valve and its changing trends with increasing sea depth are essential for SHVBS and submersibles. Actually, the dynamic characteristic is always a key index reflecting the performance of the other hydraulic valves (Dalla Vedova and Berri 2022), so it has attracted many people's attention. Jian et al. studied the stability characteristics of a spring-loaded valve with outlets by amplitude frequency characteristic analysis. The results show that increasing the spring stiffness can increase the stability of the valve (2022). Burhani et al. evaluated the static and dynamic behaviour of a direct spring-operated pressure relief valve of conical shape in the presence of two-phase non-flashing flow through experiments and a Matlab-based simulation tool (2021). Liao et al. found that large flow poppet valves are prone to water hammer and hysteresis characteristics during the working process (2015), which greatly affects the stability and rapidity of the valve. They analysed the influence of the structure on the valve through simulation and experiments (Liao et al. 2018). Alshaikh et al. predicted critical flows of a safety valve exposed to a two component (air/water) two phase flow by CFD. And the accuracy of the established fluid model has been verified (2015).
Effect of optimum process parameters in rotational-magnetorheological poppet valve polishing
Published in Materials and Manufacturing Processes, 2022
The performance of different operating parameters of the engine depends specifically on the manner of the beginning of the valve and valve designs.[12] More carbon film thickness on valve prevents thermal shocks.[13] The valve seat leakage with valve seat increases the percentage of more hydrocarbon emissions. Poppet valves are affected by thermal loading, wear, corrosion, erosion, resulting deposits, and valve burning from corrosion via exhaust surroundings, as a result of which the material’s and engine’s efficiency degrade.[14] Poppet does not properly fit on the valve seat and can cause leakage problem. A good valve seat ensures the perfect mixture of the air–fuel ratio. To ensure a proper seal, generally, the valve lapping process is used. Valve maintenance is a critical operation.[15,16] Initially, the lapping stick is used for performing the lapping operation of the valve by hand. The valve lapping paste is used for the lapping process. A particular valve lapping machine was designed for IC engines for overcoming certain issues by eliminating human intervention, reducing labor costs, and taking less time in lapping valve and valve seats.[17] Electrochemical honing (ECH) and microgrinding were used to get a higher degree of precise surface smoothness of the restoration surfaces of the engine valve face.[18] Valve seat, badly worn from grinding or pitting, can cause the failure of the valve.[12] Grinding forms circumferential fatigue loci of cracks and tool marks. The mirror-like finishing operation leads to good strength of the material even if any joints are formed.[19] The continuous smooth superior inner surface of the valve stem will enable it to resist the formation of fatigue cracks and increase the strength of valve. Reaming and polishing with abrasive paper form an amorphous layer (Beilby layer) over the surface of the internal wall of the valve. This amorphous layer causes a relatively low grade of heat transfer.[20]