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Pneumatic valves move slowly. What might be the cause?
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The core reason for the slow movement of pneumatic valves is "insufficient power (compressed air)" or "excessive resistance" to drive the valve movement, which causes the actuator to push the valve core/disc and other components to move at a lower speed.
1. Problems with the air source and air circuit system (core reason for insufficient power)
Compressed air is the power source of pneumatic valves. The air source pressure, flow rate, and air circuit smoothness directly determine the efficiency of the actuator. Problems in any link will lead to insufficient power transmission and cause slow movement.
(1) The air source pressure does not reach the rated value
The thrust/torque of the pneumatic actuator (cylinder/diaphragm type) is positively correlated with the air source pressure. If the on-site air source pressure is lower than the rated working pressure of the valve design (for example, the valve requires 0.4-0.6MPa, but the actual pressure is only 0.2MPa), the actuator output power is insufficient and cannot quickly push the valve components to move.
Common scenarios: The air compressor pressure is set too low, the pressure of the factory gas source network is unstable (the gas consumption of other equipment during peak hours causes the partial pressure to drop), the gas source pipeline diameter is too small, and the pressure loss is too large during long-distance transportation.
(2) Insufficient gas flow and insufficient gas supply
Even if the gas source pressure meets the standard, if the compressed air flow delivered to the actuator per unit time is insufficient, the actuator inflation/exhaust speed will be slow and the action will naturally be slow.
Specific reasons:
The throttle valve (such as the speed control valve) in the gas circuit is opened too small, artificially limiting the gas flow;
The gas source filter, pressure reducing valve, and oil mist collector (three-way fitting) are blocked, especially the filter element has not been replaced for a long time, which is blocked by impurities, resulting in a smaller gas path diameter and a decrease in flow;
The gas pipeline and joint specifications do not match, such as the inner diameter of the pipeline is smaller than the diameter of the actuator interface, forming a "bottleneck" and limiting the gas flow rate.
(3) There is leakage in the gas circuit, resulting in pressure/flow loss
Compressed air leaks during transmission will directly lead to a decrease in the actual pressure and flow reaching the actuator, resulting in insufficient power. Common leak locations include: the connection between the air pipe and the fitting (ferrule not tightened, thread seal failure), aging and damage to the actuator cylinder seal (leakage at the seals on both ends of the cylinder), and internal leakage caused by wear on the solenoid valve core (gas leaking directly from the intake end to the exhaust end without control).
2. Actuator Failure (Failure/Weakened Power Output)
Pneumatic actuators (cylinders, diaphragm actuators, etc.) are core components that convert air pressure energy into mechanical energy. Internal failures can directly lead to insufficient power output or operational lag.
(1) Internal wear or jamming of the actuator
Aging and wear of the cylinder piston seal: The seal between the piston and the cylinder fails, causing compressed air to leak from one side of the piston to the other ("blowby"), reducing the pressure difference between the two ends of the cylinder, reducing the thrust/pull force, and slowing down the movement;
Wear and rust on the inner wall of the cylinder: After long-term use, scratches and rust appear on the inner wall of the cylinder, increasing the friction when the piston moves, and even causing jamming, resulting in a decrease in the movement rate;
Rupture of the diaphragm actuator diaphragm: The diaphragm of the diaphragm actuator is a key component that withstands air pressure. After the diaphragm ruptures, the air pressure cannot effectively push the push rod to move, resulting in slow movement or even failure.
(2) Actuator spring failure (for single-acting actuators) The actuator of a single-acting pneumatic valve relies on a spring to achieve reset (such as automatic closing/opening when air is lost). If the spring fatigues, deforms or breaks after long-term use, the spring elasticity decreases, causing the actuator to move slowly on the "reset side" (such as the spring pushing the piston when closing the valve); Spring jam: There are impurities between the spring and the actuator housing, which hinders the spring's expansion and contraction, and also affects the movement rate.
3. Valve body component jamming (the core reason for excessive resistance)
Jamming or increased friction of the valve core, valve stem, seals and other components inside the valve will offset the actuator's power, resulting in slow overall movement. The essence is "resistance > power".
(1) Excessive friction between the valve stem and the stuffing box
The packing gland is too tight: To prevent leakage from the valve stem, if the packing gland is tightened too much, the friction between the packing and the valve stem will increase sharply, the valve stem lifting/rotation will be blocked, and the valve core will move slowly;
Packing aging and hardening: After long-term use, the packing (such as graphite packing, PTFE packing) ages and loses its elasticity. The contact with the valve stem becomes "hard friction" instead of a flexible seal, and the friction resistance increases significantly;
Valve stem rust and deformation: The valve stem is exposed to humid or corrosive media for a long time, and the surface rusts and burrs appear, or the uneven force during installation causes deformation, which increases the friction resistance when in contact with the packing, and even causes jamming.
(2) The valve core/butterfly disc and valve seat are stuck or the friction increases.
Impurities on the sealing surface: Particles in the medium (such as pipe welding slag, rust, solid particles) are stuck between the valve core and the valve seat, or adhere to the sealing surface, causing the valve core/butterfly disc to be blocked during movement and slow down the movement.
Wear or deformation of the valve core/valve seat: Long-term exposure to medium erosion and thermal deformation under high temperature and high pressure conditions leads to abnormal fitting clearance between the valve core and the valve seat, resulting in "stiffness" phenomenon and increased friction resistance during movement.
Sediment in the valve cavity: Viscous substances in the medium (such as oil, slurry) accumulate in the valve cavity, covering the valve core, valve stem and other moving parts, forming additional resistance and hindering movement.
(3) Failure of valve transmission components
The gearbox, coupling and other transmission components of the valve (components connecting the actuator and the valve stem) are worn or lack oil: wear at the gear meshing point leads to excessive transmission clearance, which reduces the power transmission efficiency; the coupling becomes loose and offset, resulting in "misalignment" of power transmission, and part of the torque is consumed; insufficient lubrication of the transmission components increases the dry friction between metals, affecting the movement rate.
4. Other external factors
(1) Low ambient temperature
In low temperature environments (such as outdoors in winter, in cold storage workshops), the moisture in the compressed air easily condenses into ice, blocking the filter, throttle valve or internal channel of the actuator in the air path; at the same time, the seals and O-rings in the actuator will harden due to low temperature, reduce elasticity, reduce sealing performance and movement flexibility, and cause slow movement. (2) Mismatch between valve selection and operating conditions
Actuator specifications are too small: The thrust/torque required for the actual operating conditions of the valve (such as high medium pressure and large valve diameter) exceeds the rated output capacity of the actuator. The actuator is like a "small horse pulling a big cart" and naturally moves slowly;
Medium viscosity/density is too high: If the valve conveys high-viscosity media (such as asphalt and viscous slurry), the flow resistance of the medium to the valve core/disc is much greater than that of conventional fluids. The actuator needs to overcome greater medium resistance, resulting in a lower operating speed.