Control & Operational Accessories
The Air filter is used to restrict any particulate matter and water from entering the air valve on the pump. The particulate can jam the shuttle or act abrasively widening the tolerances which reduce efficiency and eventually cause air slippage around the shuttle. The presence of water in the air valve mixing with the required lubricant can create an emulsion causing resistance and stalling in the shuttle, also excessive water entering into the pump air chamber can cause off centre loading on the shaft which causes early failure of the shaft and 'O' rings.
When an air pump has product in it, the loading of the diaphragm is balanced on the air and liquid sides. But when the pump is empty and the liquid pressure is nil the pump runs excessively fast causing mechanical stress to the diaphragms and early failure. The regulator should be fitted to the line and preset approximately 10 PSI higher than the required pumping pressure, this ensures minimum damage in the event of extensive dry running. The regulator is often incorrectly used for flow control, this is unsuitable due to possible changes in Head Loss caused by altering viscosity, affecting the flow rate up or down and also this usually means the air pressure is set too close to the operating pressure causing regular stalling.
The standard AODD pump requires a small amount of lubricant at approximately 10 cPs to facilitate smooth travel of the shuttle and the shaft over the 'O' rings, this prevents friction and early failure. There are now more advanced designs eliminating the need for oiling, please contact us for advice in your application.
There are four ways of controlling your AODD pump. 1) Using the regulator (see above) 2) & 3) controlling the fluid inlet or outlet. These are both normally unsuitable due to the expense of valves. 4) The cheapest and most effective method is to install a needle valve after the FRL Unit and before the pump inlet. By controlling the volume of air entering the pump you can relatively accurately control the flow and in the event of dry running the pump speed is controlled stopping the damage mentioned earlier.
When pumping slurries, after the pump has been turned off sediment can settle in the lower half of the liquid chamber. If air is supplied at full pressure instantly, the diaphragm is forced rapidly into the chamber, upon encountering the solids, the lower half of the diaphragm and plate is restricted but the upper part isn't, this causes a bending of the shaft, diaphragm rupture, or the breaking of the diaphragm plate. By introducing air slowly on start up the diaphragm has time to gently push the solids up from the bottom and into the liquid, once this has occurred the unit can build up to full flow.
Many air operated pumps require a small amount of lubrication to operate properly, this oil is introduced at the pump inlet and is atomised over the pump internals. The excess oil is expelled from the exhaust muffler along with any other particulate in the air supply. If the pump is being operated in an area where people are working they can involuntarily inhale these atomised liquids. also in clean environments a film of oil can be deposited on surfaces. To eliminate the majority of particulate, exhaust cleaners are fitted to the pump air outlet and collect them. They are also useful when pumping dangerous or expensive products as often with diaphragm failure liquid can be forced to the pump exhaust. See Spillstop®
The above equipment should be installed with every pump installation individually and as the cost is less than that of an air valve, it is probably the best preventative maintenance you can give your production.