Support, Wet Vacuum Pumps, Frequently Asked Questions

Q: What is a wet vacuum pump anyway?
A: A wet vacuum pump, commonly called a wet pump, is a vacuum pump that is internally lubricated by engine oil. All engines since the age of time, already have the accessory cases drilled for a wet pump so no additional modifications are needed from the installing mechanic.
Q: What’s inside of a dry pump?
A: A dry pumps uses a cheap aluminum casting to hold the internal parts. Inside you will find nothing more than a solid block of hard graphite [pencil lead] that has 6 slots cut into it at an angle which allow 6 thin graphite blades to slide in and out of these slots and rub up against the inside of the aluminum pump, creating a vacuum during rotation. No bearings, nothing else. They are extremely brittle and are intolerant to rubber flaking off from the inside of the vacuum hoses, engine backfires, or even turning the prop backwards. One minute they might be working fine, the next second, proof, all you have is a bunch of pencil dust.
Q: What’s inside of a wet pump?
A: A wet pump consist of a solid billet aluminum housing to hold all the parts. Inside is a hardened steel rotor supported at each end by highly precision ball bearings. This steel rotor has (4) precision ground slots which hold (4) oil impregnated soft graphite blades which can rotate clockwise or counterclockwise with no adverse effect. When the pump rotates, these blades are in constant contact with a cast iron liner that has been precision honed to a mirror finish. All these internal parts are machined and ground to within .0002” [two ten thousands of an inch] tolerance. Then all the parts are assembled and shimmed for maximum performance. We even break it in for two full hours on our test stands just to make sure it operates flawlessly.
Q: How long have wet pumps been around?
A: The original Pesco wet pumps were patented on January 26, 1937, and were prevalent in the 1940s to the late1960s. In the early days, you could not find an aircraft that did not have a wet pump installed.
Q: Why did they disappear?
A: Airborne came out with a great marketing scheme in the early 1970s, which touted a lighter, “cheaper” vacuum pump and the market bought into the hype. You can see where cheaper got all of us. Airborne is no longer in the vacuum pump business, and we have pilots getting killed when they fail.
Q:I heard that wet pumps blew lots of oil all over the aircraft, is this true?
A: No, not really. Now remember wet pumps are lubricated by engine oil. They will naturally mist oil out the discharge side of the wet pump at a rate of 20-50 cc /hr. While this is surely not pouring out oil from the engine, it can coat the engine compartment with a thin film of oil which collects dirt. We purchased the Walker AirSep division a couple of years ago to solve this problem. Walker Engineering made an outstanding Air Oil Separator that cleaned up the oil that the engine spit out AND collected the oil from the wet pumps with one device. It is not mandatory that you purchase an AirSep for your airplane, but you will have to contend with this oily film. Aviation is all about compromise.
Q: What does my mechanic have to do to install your wet pump?
A: Remove the existing dry pump, install a new gasket that we supply in the kit, tighten the (4) 1/4” nuts which hold the pump to the accessory case, transfer the low loss fittings from the old pump to the new pump, and hook up the existing hoses.
Q: Is that all there is to it?
A: That’s all folks.
Q: Is there anything else you recommend we do during the installation?
A: Actually there is. We live by the saying ”Do it right the first time”. While we cannot force the mechanic to do, we are highly recommending all the rubber hoses connecting our wet pump to the main vacuum system are replaced. Rubber hose is inexpensive and this is a perfect time to do it. Also the garlock oil seal in the rear accy case should also be replaced at the same time.
Q: Why should I want to do this?
A: Rubber naturally dries out and gets brittle over time. Given the fact that the vacuum hoses could be 5, 10, 15, or even 20 yrs old, it is a perfect time to start fresh. And, mechanics almost never think about replacing the garlock oil seals in the accy cases so there is no telling how old this oil seal is.
Q: How long is the warranty period on your wet pump?
A: 10 yrs or 2,000 hrs, whichever come first.
Q: How can you possibly offer such a long warranty?
A: We think it is a pretty safe bet. Wet pump reliability has thoroughly proven itself over the past 60 yrs. We have spent 8yrs making sure our wet pump is perfect. Not close… perfect!
Q: Are there any requirements to validate your warranty?
A: Yes, there are two things. The fittings that are used to connect our pump to the vacuum system must be “low loss” fittings. Most modern aircraft already use “low loss” fittings, but we see some older aircraft using normal AN fittings. AN fittings have abrupt 90 degree bends instead of sweeping bends in low loss fittings. This makes the pump work harder and is very inefficient. In addition, the engine must have an oil filter installed. These are highly precision pumps and they must have filtered oil running through them.
Q: Does it matter it my current pump turns clockwise or counterclockwise?
A: That’s what makes wet pumps unique. They don’t care which way they turn. Just so long as they go round and round, they are very happy.
Q: Is there any normal maintenance I need to do on this pump?
A: Nope, nothing at all. Just fly the airplane.
Q: Are you going to be offering any device or light that will tell me when you pump is working?
A: Yes we will. As soon as we finish certification of the pump, we will be offering a dash light that will come every time you turn on the aircraft master switch. It will go out as soon as your pump is producing at least 3.5” of suction on the gauge giving you piece of mind that our pump is working just fine.
Q: How much does it cost?
A: For any orders received before we receive certification, we are offering an introductory price of $1,500. After certification the price will be $1,795.
Q: Why so much?
A: This is a high precision part that is very expensive to make. You could replace your vacuum gyros with electric gyros for a lot more money and knock 15 lbs. of useful load off the aircraft. You could also spend $2,500 for a standby electric system but all you get is an electric motor connected to yet another unreliable dry vacuum pump. A little bit better than nothing, but not much.