Overview of Aircraft Pumps
The first airplanes did not come equipped with such technology like vacuum pumps installed on them. On the contrary, the suction that was needed to manage the inner gyro equipment was supplied by a venturi tube that was placed on the outside of the aircraft. Venturi tubes were simple and manageable but they did come with many disadvantages because it was so dynamic, meaning the aircraft was forced to be constantly moving at a fairly high speed to develop enough vacuum to run the instruments. Not only that but this tube needed to rotate the gyros before the venturi could start being used and it left the system exposed to the elements. What eventually solved this problem was the engine-driven vacuum pumps which we’ll go over more in detail below.
When first engineered, these vacuum pumps were known as wet pumps because they ran on hydraulic pumps that would pump liquid instead of air. Engine oil would be used to lube up the pumps which helps the internal parts become more resistant to wear than dry pumps. This lube, however, also contributes to air expelling out of the exhaust port of the pump. Air-oil separators were used on the pump’s exhaust port to try to capture the oil. Unfortunately, some oil would usually bypass the separator, resulting in oil residue on the engine and aircraft exterior.
It wasn't until the late seventies that pumps became more engine driven and less reliant on oil to lubricate the vanes of the pump. The carbon vanes of dry pumps are smaller in thickness than those on wet pumps. The vanes wear as they rub against the internal wall of the stator (or center section of the pump). As the vanes wear, they create a light carbon dust. This dust provides "self-lubrication" for the vanes.
The length of the vanes decreases over time through normal wear. If these vanes wear too much, the vane can bind in the rotor causing them to break. Until recently, mechanics had no way of determining the extent of vane wear. Recent designs in dry pumps have added the ability to determine vane life. Now, both Rapco and Tempest incorporate some type of wear indicator into their pump, thus ensuring the pump’s vanes have an adequate service life remaining. One of the biggest contributors to vacuum pump failure is contamination. This contamination can be fluid contamination. Mechanics must be diligent in preventing contamination from damaging the pumps. Foreign particles larger than 0.001 inch can cause damage to your pump. It is necessary to keep the entire pneumatic system clean. One of the biggest contributors to vacuum pump failure is contamination. Mechanics must be diligent in preventing contamination from damaging the pumps. Foreign particles larger than 0.001 inch can cause damage to your pump. It is necessary to keep the entire pneumatic system clean.
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