Dry Air Pumps - Frequently Asked Questions

Q: Which Dry Air Pump is correct for installation on my aircraft?
A: Please refer to the application chart on the dry air pump page to find the correct pump for your aircraft. If you or your mechanic will supply us with the aircraft make, model and engine type, we will be happy to provide you with the applicable pump for your aircraft (call 1-800-822-3200 or e-mail gehrlich@aeroaccesories.com). 

Q: Is an overhauled Dry Air Pump as good as a new pump?
A: We can only speak for our own overhauled pumps since we have no control over the quality of other overhaul shops. Before Aero Accessories, Inc. offered an overhauled pump, we spent more than a year in research and testing to determine what was required to produce a quality overhauled pump which would last as long as a new pump producing the vacuum or pressure required for aircraft application. In 1984 Aero Accessories, Inc. had its overhaul process specification approved by the FAA and began offering quality overhauled vacuum pumps to general aviation. We take great pride in our state of the art overhaul facility, and produce the best overhauled pump on the market today. Over the years we have acquired FAA-PMA's for all component parts of the Dry Air Pumps, and have supplied replacement parts to all overhaulers world wide.

Q: When I start my engine the vacuum gauge reads zero vacuum, but as the engine RPM increases, the gauge will indicate vacuum. What causes this?
The carbon vanes inside the pump are sticking in rotor slots. Oil or solvent has entered the pump either from a bad oil seal in the engine case at the pump mounting area, or from pressure washing the engine with an oil-based solvent (spraying directly on the pump). The oil or solvent will work its way up into the pump through the drive end, mixing with graphite dust and turning into a paste like material.

A Dry Air Pump is just that: DRY. As the carbon rotor and vanes wear, they produce graphite dust which lubricates moving internal parts of the pump. When oil or solvent mixes with this graphite dust, it keeps vanes from moving freely in their slots and they stick. At low engine RPM, the vanes are recessed in their slots and create no vacuum, but as engine RPM increases, centrifugal force slings the vanes out, allowing them to grab air and create vacuum. Once a pump has become contaminated, its life expectancy is extremely short. The cause of pump contamination should be determined and corrected and the pump should be replaced as soon as possible. 

Q: What procedures should be taken when replacing a failed pump?

A:  (1) A correctly functioning pump creates a vacuum in the system lines, so when the pump fails (due to wear or from FOD which has entered pump) the carbon rotor and vanes break into very fine pieces which can be sucked back up into the inlet hose. It is very important to remove the inlet and outlet hoses from the aircraft and clean them out thoroughly, making sure to remove all particles. It is imperative to clean the entire system after a pump failure. By doing so you will eliminate the chance of premature failure by your new replacement pump as a result of carbon FOD from a previously failed pump entering your new system.

(2) After you have installed the new replacement pump, check and make sure the aircraft vacuum system is working properly. A faulty regulator , dirty vacuum pump filter, or a crimped or partially collapsed hose which causes a restriction in the system can force to pump to work harder, causing premature failure.

(3) If your aircraft engine is high time, go ahead and replace the oil seal in engine case where the pump mounts. The area could be dry now, but the seal could start leaking in just a few hours causing oil contamination in your vacuum pump, making it inoperable. Less than $10 dollars spent here could save you hundreds of dollars later.

Q: I frequently need to replace my Dry Air Pump. What could be causing this?

A: 1. Check your hoses to make certain that they are not collapsed or kinked.
2. Replace the system filter(s). A dirty or clogged filter will cause the pump to work significantly harder than normal and could cause premature failure.
3. Make sure that you have the correct pump installed on your aircraft.
4. Make sure that no oil contamination is entering the pump.

Q: Should I use a cooling shroud on my dry air pump?

A: Yes, using a cooling shroud whether on a 200 series or 400 series dry air pump can reduce pump temperatures by as much as 10%.  If  you are interested in purchasing a cooling shroud please contact McFarlane Aviation