Why do most cylinders use exhaust throttle instead of intake throttle?

The exhaust throttle mode makes the exhaust cavity have a certain back pressure, which is beneficial to control the stability of piston movement speed; However, the intake throttle can only be adjusted by adjusting the intake flow, which is unstable and the pressure in the exhaust chamber is small, which is easy to cause speed fluctuation and is not conducive to control.

Of course, in an ideal situation, the intake throttle and the exhaust throttle can achieve the same goal, but the actual situation is that the movement of the piston in the cylinder will always be rubbed, and leakage will occur, and the friction is unstable during the stroke, so sometimes there will be crawling and other phenomena. Therefore, exhaust throttling usually works better.

The medium velocity between the throttle plate and the valve seat is very high, which leads to the surface damage of these parts quickly, which is called cavitation. In order to minimize the influence of cavitation, the disc is made of cavitation resistant material (alloy steel) into a streamlined cone with the apex angle of 140 ~ 180, which can also make the disc have a larger opening height. Generally, throttling in a small gap is not recommended.

Extended data:

Flow valve and one-way throttle valve are simple flow control valves. In the hydraulic system of the constant displacement pump, the throttle valve and the overflow valve together form three kinds of throttle speed regulation systems, namely, the oil inlet throttle speed regulation system, the oil return throttle speed regulation system and the bypass throttle speed regulation system.

Throttle valve has no negative feedback function, so it can't compensate the speed instability caused by load change. Generally, it is only used in situations where the load changes little or the speed stability is not required.

Charged polarized molecules are generated after oil aging or pressing, and there is a potential difference on the metal surface of the throttling gap, so the polarized molecules are adsorbed on the surface of the gap, forming a solid boundary adsorption layer, and the thickness of the adsorption layer is generally 5~8 microns, thus affecting the size of the throttling gap. When the above deposits and adsorbents grow to a certain thickness, they will be washed away by the liquid flow and then re-attached to the valve port. In this way, the pulsation of flow is formed.

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