Pneumatic throttle knowledge

First, the pneumatic throttle valve function:

The function of the pneumatic throttle valve is to change the flow area of the relevant valve port and control the flow rate. (Load change, the pressure difference before and after the valve does not change)

1. Requirements: Sensitive and reliable, stable work, no noise, simple mechanism.

1 When the pressure difference before and after the valve changes, the flow rate through the valve changes little;

2 When the oil temperature changes, the flow change through the pneumatic throttle valve is small;

3 It is necessary to have a large flow adjustment range, which is not easy to block at a small flow rate.

4 When the valve is fully open, the pressure loss of the liquid flow through the pneumatic throttle valve is small;

The leakage of the 5 valve is small.

2. The form and characteristics of the throttle:

The orifice is the key part of the flow valve, and the form of the orifice and its characteristics largely determine the performance of the flow control valve. Several commonly used throttle ports are shown in Figure 7.2.

(1) Needle valve type throttle. When the needle valve is moved axially, the size of the annular passage is adjusted, thereby changing the flow rate. The structure is simple to process, but the throttle port has a large length, a small hydraulic radius, is easy to block, and the flow rate is greatly affected by the change of the oil temperature, and is generally used in occasions where the demand is low.

(2) Eccentric throttle. An eccentric groove with a triangular (or rectangular) cross section is opened in the spool, and when the spool is rotated, the passage size can be changed, thereby adjusting the flow rate. The eccentric groove structure should be avoided due to the radial imbalance of the valve core.

(3) Axial triangular trough throttle. One or two inclined triangular grooves are formed at the end of the spool, and axial movement of the spool can change the flow area of  the triangular groove to adjust the flow. The hydraulic radius of the axial triangular trough orifice is large. Good stability at low flow rates. In the high pressure valve, two inclined faces are sometimes milled at the shaft end to achieve throttling.

(4) Slot type throttle opening. The valve core is provided with a slit, and the oil can flow into the inner hole of the valve core through the slit and then flow out through the left hole. The rotary valve core can change the flow area of the slit. This orifice can be made into a thin blade structure to achieve a small steady flow, but the spool is subject to radial imbalance and is therefore only suitable for use in low pressure pneumatic throttles.

(5) Axial slit type throttle opening. An axial gap is formed in the sleeve, and the axial movement of the valve core can change the flow area of the slit. This orifice can be made into a single thin blade or a double thin blade structure, and the flow rate is not sensitive to temperature. The hydraulic radius is large at small flow rates, so the stability at low flow rates is good, so it can be used in applications with high performance requirements (such as speed control valves). However, the orifice is easily deformed under the action of high pressure, and the rigidity of the structure should be improved during use.

Second, the simple pneumatic throttle valve

The so-called simple pneumatic throttle valve usually refers to a pneumatic throttle valve that is difficult to adjust under high pressure. Because it does not balance the hydraulic pressure acting on the pneumatic throttle spool, when operating under high pressure, the adjustment torque is very high. Large, and therefore must be adjusted without pressure (or low pressure). Conversely, the adjustable pneumatic throttle valve is easy to adjust under high pressure, which balances the hydraulic pressure acting on the spool, so no matter what working condition Adjust underneath and the adjustment torque is small.

Third, the performance requirements of the pneumatic throttle valve:

(1) The flow adjustment range is large, and the flow rate-pressure difference changes smoothly;

(2) The amount of internal leakage is small, and if there is an external leakage port, the amount of external leakage should be small;

(3) The adjustment torque is small and the action is sensitive.

Fourth, the classification and working principle of pneumatic throttle valve

A pneumatic throttle valve is a valve that controls the flow of a fluid by varying the throttle section or the throttle length. The pneumatic throttle valve and the check valve are connected in parallel to form a one-way pneumatic throttle valve. Pneumatic throttle and one-way pneumatic throttle are simple flow control valves.

In the fixed pump hydraulic system, the pneumatic throttle valve and the overflow valve cooperate to form three throttling speed control systems, namely, the throttle throttle throttle speed control system, the return oil throttle throttle speed control system and the bypass throttle flow. Speed control system.

The pneumatic throttle valve has no negative flow feedback function and cannot compensate for the instability caused by the load change. It is generally only used in applications where the load does not change much or the speed stability is not high.

According to its function, the throttle function has a pneumatic throttle valve, a one-way pneumatic throttle valve, a precision pneumatic throttle valve, a throttle stop valve and a one-way throttle stop valve, etc., according to the structure of the throttle port, Pneumatic throttle valve has a needle type, undercut groove type, eccentric groove type, cone valve type, triangular groove type, thin blade type, etc.; according to its adjustment function, the pneumatic throttle valve can be divided into simple and adjustable Two.

The structure and function symbols of the pneumatic throttle valve are shown in the figure. The pressurized oil flows in from the oil inlet P1 and flows out from the P2 through the orifice. The orifice is in the form of an axial triangular groove. The force acting on the pneumatic throttle spool is balanced, so the adjustment torque is small, and it is easy to adjust under high pressure. When adjusting the handwheel of the pneumatic throttle valve, the pneumatic throttle spool can be pushed down through the plunger. Moving, the reset of the pneumatic throttle valve core is realized by the spring 5, and the up and down movement of the pneumatic throttle valve core changes the opening amount of the throttle opening, thereby realizing the adjustment of the fluid flow rate.