COMMON QUESTIONS ABOUT DIAPHRAGM PUMP
- What is the heaviest most viscous material that can be pumped?
The more viscous the fluid being pumped, the slower the pump should stroke. Use the air control valve to slow the air flow of the pump.
- What is cavitation and how do I stop it from happening?
- Is there any advantage to "oil-less" vs. lubricated air valve?
The greater issue in valve selection is the valve performs throughout the full range of conditions that the pump is expected to perform. For example, will the pump cycle at a rate necessary for the pump to deliver its full rated output? This might be as low as one stroke every several minutes or even discharge shut off completely for hours with the pump under pressure. Upon reopening the discharge, the pump should begin pumping with no interruption.
Compressed air preparation is as important to long term trouble free operation as using the right kind of oil for your car and changing it on a periodic basis. Some people routinely get 150,000 miles Out of a car, others are having problems at 30,000 miles. Proper care and maintenance is usually the difference. Proper air preparation amounts to using a filter, regulator, lubricator in the air supply line. Use a good grade of SAE 10 grade oil or lighter. Do not use a multiviscosity motor oil. The oil should be fed at a rate of one drop every 20 SCFM. That would be one drop per minute if the full were pumping at maximum flow at maximum air pressure. The filter should remove dirt as well as water from the supply air. However, the filter should be emptied or left open to bleed the trapped water out of the system. Too high viscosity oil or water mixed in with the oil will cause the valve to shift slowly or irratically.
A quick check of the lubrication quality would be to remove the lower cover of the muffler, remove the screen, then feel the screen. The screen should have a thin light film of oil. If the oil is heavy, gummy or milky colored it is probably to high viscosity or contains water. If the air is contaminated with dirt, the dirt will also show up in the muffler.
- Do plastic pumps always leak?
- No, however they must be inspected and retightened more often then a metallic pump. Plastic materials by definition, flow or deform whenever they are put under Stress. This deformation happens even faster at higher temperatures. This is best illustrated by clamping two plastic parts together with bolts and tightening the bolts to, for example, 50 inch pounds torque. In 48 hours it is likely that the clamping torque would have decayed to about 35 inch pounds. If the same part were retightened to 50 inch pounds torque then looked at again in 48 hours it would again have decayed to about 35 inch pounds. This process can be repeated again and again until the plastic has completely flowed away from under the bolts. With proper design, selection of materials and installation, this cold flow or creep will not impair the function of the pump, but does require some added maintenance especially at high pressures and high operating temperatures. Bolts, nuts, ring clamps and press fits are all subject to this kind of cold flow or creep.
Some air leakage may occur around the valve assembly or Out the exhaust port when the pump is pressurized but with discharge closed. This would be air bypassing the shifting members. That leakage should total less than 0.15 SCFM.
- Should I use an air pressure control or a throttling valve to adjust pump speed?
- How can I get a uniform non-pulsating discharge?