The collector was shipped with the pilot solenoid boxes being shipped separately. The service engineer came to start up the collector. When the compressed air was piped up and the main valve opened, the pressure would not build up in the manifold. Examination of the piping revealed that the wrong ports in the solenoid valves at the solenoid enclosures were connected to the valves. This kept all the solenoid pilot valves open to atmosphere causing all eight diaphragm valves to open at the same time. The compressed air supply was not sufficient to allow even one diaphragm valve to be opened continuously. The connection is sized to provide air to supply a single valve to run no more than a 10% duty cycle.
The service engineer connected tubing to the correct ports from the solenoid valve enclosures. After that was complete, the compressed air supply was again turned on. Again the pressure in the manifold would not increase enough to pressurize the manifold. From the sound of it, at least one diaphragm valve was open. To determine which one(s) was the culprit, he checked the ports that were open to atmosphere and found the solenoid valve that was open. He squeezed the flexible tubing leading to that valve and the valve de-energized and pressure built up in the manifold to 85 psig. He replaced the tubing and the collector started pulsing.
He next listened to the pulse. It had a hissing sound when the diaphragm valve was opened. The gauge on the manifold dropped to below 15 psig. Both of these symptoms indicate that a valve is open too long. (On the control panels it is usually a pot adjustment and labeled “on time”). This “on time” should be adjusted to the minimum time that shifts the diaphragm valve. All cleaning of the bags takes place in 5 milliseconds after the valve completely opens. It takes a valve 10 to 70 milliseconds to fully open depending on the valve used. The sound should be more like a thumping noise. The pressure in the manifold after each pulse should be no less than 50 psig. This proper adjustment of the “on time” often reduces air consumption by 50 to 90%.
Other General Considerations
Another cause of these symptoms may be debris in the compressed air line. In connecting the compressed air supply to a pulsejet collector often new piping is installed. In the process of threading the pipes and installing fitting shavings may accumulate in the piping. Sometimes the air line filter is installed far away from the dust collector. If these shavings get into the collector valves they may clog up the internal vent port in the diaphragm valve and get into the actuator on the solenoid valves causing them to stay open. Before the piping is hooked up to the manifold on the collector, the pipes should be blown clean. The pulsing may cause the shavings to gradually move down the pipes and not show up until a few days after start up.
Another possibility occurs when it is noticed that diaphragm valves require frequent replacements of the diaphragms and the spools in the pilot solenoid valves also require unusually high replacement. It is possible the air line lubricant has the incorrect fluid and will attack the sealing materials. These valves are good for at least 100,000 cycles which is 4-5 years for a single shift operation, 5 days per week.
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