Aerotech

Unless you fly in excess of 150 hours a year, I doubt that your problem is the air pump. Most newly manufactured air pumps will last between 600 to 800 hours. Unless your pump has worn excessively do to an overload problem, I would check your system before any thought of a flat-out pump replacement.

I noticed that you mentioned “vacuum” along with Fallon, Nevada.

This brings to mind a problem we solved in Carefree AZ, concerning a Mooney aircraft. Seems that the connecting hose between the gyro instruments and the vacuum gage was surgical tubing. With the extremely dry weather in that area (Phoenix, AZ) the tubing had deteriorated to the point that a vacuum could not be maintained in the system. Replacement of the surgical tubing with 1/4 in pneumatic hose solved the problem. Total cost $3.56.

This situation was reported in the April issue of the MAPA Log. (Mooney Pilots Association Magazine). A close-up on the failed surgical tubing is shown here. Notice the gage connection

Regardless of what model aircraft flown, a decrease in vacuum or pressure during climb is usually an indication of a deteriorated hose, loose hose clamp or even a cracked and leaking indicator gage. There are a lot of items to check before pointing a finger at the
air pump. What ever you do:

Do not adjust the regulator in an effort to fix this problem!

Regulator adjustment in this case would only shorten pump life.

Let us know what you find and
Fly “Heads Up“,

R. Heysek
Aerotech Components, Inc.

For a complete (down-loadable) outline on the operation and testing of “Vacuum” or
“Pressure” gyro instrument systems, see our section entitled “Data Sheets”.

I always preach about fixing the system and leaving the vacuum regulator alone. Only in this case, that very well may be where your problem exists.
When an air pump fails there are a lot of carbon parts (rotor & vanes) breaking and grinding going on just prior to the flexible coupling separating. As long as the rotor continues to rotate all the dust and carbon particles are vented out the exhaust port of the air pump. However, a point comes when the broken rotor and vanes will bind in the housing causing the coupling to shear. At that instant, (pump not rotating) the positive air pressure you have in the engine compartment combined with the vacuum remaining in the gyro instruments may cause some carbon dust and small particles to travel “up-stream” towards your gyro instruments. The first obstacle they have to pass of course is the vacuum regulator.

Check your vacuum regulator for any debris that might have gotten caught between the bottom diaphragm washer and the diaphragm seat. If the diaphragm is held open and cannot oscillate, your system vacuum will increase and decrease with engine/pump rpm.

Always clean out the inlet hose when installing a new pump. Any carbon dust or debris left in the line from the failed pump will travel into the new pump as soon as you start the engine. Pumps and time are expensive. Spend your money on only one pump and your time in the air!

Other causes and symptoms of a typical 2H3-[ ] vacuum regulator failure can be found in the Aircraft Pneumatic System Data section of our web-site.

In this case, I believe your solution is a simple regulator cleaning or replacement.

For a complete (down-loadable) outline on how to test your system for proper operation see our section entitled “Data Sheets”.

Let us know what you find and

Fly “Heads-Up”,

R. Heysek
Aerotech Components, Inc.

With all the components that can fail within your gyro system none can “repair” themselves by the time you get to the end of the runway, except the air pump. The only thing changing from the time you start your engine to the time you’re ready for the wild blue yonder, is the temperature of your engine.

My thought on this is somehow either oil, cleaning solvent or moisture was ingested into your pump.

The air pump interior contains carbon vanes positioned in slots in a carbon rotor. As the rotor spins, centrifugal force throws the vanes out against the interior wall of the pump housing to create a vacuum on the backside of the vane. With the rotor spinning at a high rate of speed the 6 vanes create enough vacuum in the system to eventually operate your gyros. The vacuum regulator not only smoothes out these “pulses” of the pump into a steady vacuum source but also regulates the amount of vacuum applied to your system as the engine and pump may vary in speed.

The vanes are lubricated in the vane slots by carbon dust. This super lubricant is fine for the purpose intended except when mixed with any liquid contaminate. Take a little carbon dust mix in a little liquid and you get the blackest “honey like” substance ever made. Add a little liquid to the pump interior and the vanes start to stick within the slots. With one or two vanes not producing a vacuum, the pump is now creating a pulsation in the system that the regulator cannot correct. Thus, needle “bounce” or vibration.

If the contamination were water (condensation), running the engine several minutes would evaporate the water, dry out the pump interior and your back in business.

If the sticking vanes were cause by oil or solvent ingestion you’re not as lucky. Pump replacement is the only answer, but only after you figure out the source of contamination.

Cleaning Solvent – Cover the air pump coupling every time you spray clean the
Engine.

Oil – Make sure:

1. You have a good air pump gasket at the pump mounting.
2. You don’t give the pump an oil bath when you change that old oil filter can.

Let us know what you find and Fly “Heads-Up”,

R. Heysek
Aerotech Components, Inc.

Even though the deice control valve (in your case a model 2H22 valve) was electrically disconnected, pressure in the system is still controlled by the first stage of that regulator.

A cutaway diagram of the 2H22 valve has been copied from the “Data Sheet” section of our web site for your reference here.

During normal flight, airflow from the air pump enters the 2H22 valve at the “Low Pressure” regulator side of the valve. Part of this airflow (containing carbon dust contamination) moves upward through the rivet assembly orifice, into the inner chamber of the solenoid where it passes just below the plunger assembly before making a 180 degree turn. This airflow is then exhausted thru two small vent ports in the bottom of the solenoid.

Airflow through the valve body, thru the rivet orifice, into the solenoid for venting overboard is continuous. With the solenoid plunger assembly being spring loaded in the up position, disconnecting the electrical leads to the solenoid would result in the same airflow as if the solenoid was connected but with no power applied. As carbon contamination accumulates inside the solenoid, less air is vented overboard and more air pressure is applied to the top of the diaphragm assembly. With air pressure pushing the regulator diaphragm closed, less system air pressure is vented overboard creating higher backpressure against the air pump and making the manual valve adjustment redundant.

Eventually if the valve solenoid is not cleaned and becomes completely blocked, (same action as electrically actuating the solenoid) system pressure will build to deice boot pressures limited only by the pressure setting of the valve second stage (21-23 psi). Air pumps continually operating at high system pressures may fail in less than 30 minutes. Unfortunately the pilot has no indication of any problem occurring since the gyro instrument pressure gage in the cockpit only indicates the pressure drop developed across his gyro instruments (4.7-5.2 in Hg.).

Frequent examination of the 2H22-[ ] valve for excessive amounts of carbon contamination of the first stage is a rewarding experience that might prevent the untimely failure of an air pump.

As you have already experienced, installation of the CV1J4 “Clear View” inline air filter will provide an effortless method of monitoring the amount of carbon dust being emitted from the air pump. High carbon discharge means high system pressure and a problem, which if not solved, will fail an air pump.

Always check the aircraft pneumatic system with a test kit (CV-700 or equivalent) rather than running the engine and recording the value on the instrument panel vacuum or pressure gage. Since the instrument panel gage is connected across (parallel to) one of the gyro instruments, it is an indication of gyro instrument values not system values.

One of the main statements made during my pneumatic systems seminars is:

“Running the engine to check proper pneumatic system operation only
confirms the needle in the vacuum\pressure gage has not fallen off its axial.

Proper system operation is only confirmed by knowing exactly what pressures (or vacuum) has to be created at the pump connection in order to obtain the reading on the panel instrument gage.

Running the engine all day, will not give you that information!

We thank you for your information.

It looks like you’re on the road to solving your problem. If there is anything else we can help you with in the future, please don’t hesitate to call.

We will pass this information on to others that have deice systems on their single or twin engine aircraft, just in case they also are experiencing short air pump life.

Regards,

R. Heysek
Aerotech Components, Inc.

Mr. D.,

Before we point a finger at the FBO or air pump manufacturer, let’s look at a few things you can check on your aircraft.

Since you didn’t mention the air pump model number, I assume you have a model 212 (warranted for 1000 hours) or a model 242 (normally warranted for 400 hours). Either way, your air pumps are operating well below the curve.

Being your aircraft is an older model, the first thing I would check are the hose clamps, both in the engine compartment and behind the panel.

When first installed, ‘Spring Clamps” are quick and easy, preventing pressure or vacuum leakage at the connection
	Due to normal aging of the hose, especially under adverse conditions in the engine compartment, the hose will deform and become loose on the air fitting. Since there is no way to “retighten” the clamp, pressure/vacuum from the system is lost.
Bottom Line ! If you have “Spring Clamps” at the hose connections, replace them with “Screw Type” clamps.

A pressure gage reading of 5.0 Hg. is only equivalent to 2.5 psi., a small pressure that can be affected by many small and seemingly insignificant leaks.

While you’re inspecting behind the panel, also make sure someone hasn’t replaced the pneumatic hose with surgical tubing, another problem we covered in Q & A #1.

For additional information on the proper procedures in checking your aircraft and increasing air pump performance, go to the DATA SHEETS section of our web site, click on “Pressure Systems” and then select “Operation & Testing.

R. Heysek
Aerotech Components, Inc

I just had an air pump failure on my aircraft in less than 30 hours even after a cooling shroud was installed. After seeing your website I thought I would contact you for a possible solution. Have you heard of this type of quick time failure in the past?? -Bob G., Columbus, OH

Mr. G.,

After our phone conversation and receipt of your failed air pump, photos were taken that indicated the cause of your failures. With your permission, we have included some photos in this article so other pilots or owners might be aware of the situation. For those that are not familiar with the air pump manufactured by Sigma-Tek (see adjacent photo) we insert the following.

Design of the Sigma-Tek aluminum rotor pump however created a new problem. When internal temperatures increase the diameter of the aluminum rotor also increases. As long as the air pump housing increases it’s internal bore size with this rotor size increase, there is no problem. However, with high flying aircraft like the Beech F33, Cessna 210, Mooney 231 or 252, the engine compartment can operate at a relatively cooler temperature, which means the aluminum housing will not experience the same expansion rate as the internal rotor. This problem was first identified in the field with the introduction of Mooney 252 aircraft in the late 80’s, their owners usually flying at the higher altitudes.

Examination of your air pump, even though not installed on a high-flying aircraft, resulted in the same failure. Installation of a cooling shroud on the Sigma-Tek air pump reduced pump bore expansion while at the same time internal pump temperatures caused the rotor to increase in size. You can see the results in the adjacent photo, abrasion of the rotor and in the close up picture of the pump interior, bore damage from the fast spinning, expanding rotor.

Rubbing of the rotor with the internal bore causes a continued increase in rotor temperature, the rotor expands even more until binding occurs and the rotor shaft (or coupling) is sheared due to the force of engine rpm. (You are not going to slow the rotation of a 200 hp aircraft engine!)

During our conversation, you did mention that the first sign of trouble was a bouncing movement of the vacuum gage needle, that gradually got more erratic until pump failure occurred and the needle fell to ‘0.” That erratic bounce was the first sign the aluminum rotor was scuffing the inside of the pump bore. However, at that point, I don’t believe there was anything you could do except realize you were about to have an “in-flight air pump failure”!

My Advice!

If your air pump is failing do to an overheating condition caused by faulty system components or air leaks, check the system for proper operation as outlined in the “DATA SHEETS“ section of this website.

If you decide to go back to the carbon rotor, carbon vane type air pump I would still suggest you check your system for proper operation. If you have read any of the Q & A articles posted on this web site you know by now that an engine run-up and visual check of the vacuum or pressure gage does not indicate what pressures your air pump is generating.

Regardless of which air pump you purchase,
Check the pneumatic system with shop air
and the proper test equipment,
Before you install the next pump!

Fly “Heads-Up”,
R. Heysek
Aerotech Components, Inc.

We have a Piper PA-34-200T that indicates a loss of instrument pressure during cruise. The vacuum gage operates correctly on the ground during magneto check (pulling in both “eye-ball” indicators), but at altitude, the port engine “eye-ball” is visible most of the time. What can be causing this problem? -Ken, Anchorage, Alaska

During a visit to their facility, the CV-700 Pneumatic Test Kit was used to check the complete aircraft pneumatic system as outlined in the CV-700 Instruction Manual. The results are discussed below.

The pressure line from the port air pump was removed and connected to the CV-700 regulator and hose adapter. Inline pressure was measured by a pressure gage probe inserted into the aircraft system hose. With shop air then applied to the CV-700 test regulator, the regulator adjustment knob was slowly turned to apply pressure to the aircraft system.

4. Air immediately started venting from the 2H30-16 pressure regulator at an applied pressure as low as 0.5 psi (1.0 in. Hg).

• Note:  A properly operating pressure regulator would not vent air pressure from the system until pressure had reached gyro instrument pressure of approx. 4.8 to 5.2 inch Hg. (2.4 to 2.6 psi). This “set point” pressure is outlined in the aircraft maintenance manual.

5. Adjustment of the 2H30-16 regulator via the adjustment screw had no effect on decreasing the release of air from the valve.

The valve was removed from the aircraft and bench tested as follows.

1. Short sections of pneumatic hose were secured to the inlet and outlet of the 2H30-16 regulator.

The hose attached to the outlet side of the valve was plugged to prevent air leakage. The inlet hose was connected to the CV-700 pressure regulator. To monitor the value at which the 2H30-16 valve diaphragm raises and starts to release pressure, the needle of pressure gage assembly (CV-G30) was inserted into the inlet hose.

• A multimeter was attached to the 2H30-16 switch contacts to monitor proper operation.

2. Shop air was connected to the CV-700 test regulator with the adjustment knob turned counter-clockwise. (no pressure applied to the 2H30-16 valve)
3. The CV-700 regulator “On/Off” slide switch was move to the “On” position.
4. The CV-700 adjustment knob was turned slowly clockwise applying air flow and pressure to the 2H30-16 valve.
5. The 2H30-16 valve immediately started dumping air overboard at less than .5 psi (1 in. Hg.).

• Any attempt to prevent air loss from the 2H30-16 valve with the diaphragm adjusting spring was un-successful.

Examination of the 2H30-16 valve diaphragm assembly showed evidence of wear and scoring, requiring replacement with a new 2H30-16.

With the aircraft now officially “down for parts” and off the flight schedule, time was available to test the pneumatic system on the starboard engine.

Tests conducted as outline in the CV-700 Test Kit Manual resulted in identical results as those indicated above for the port engine.

The starboard 2H30-16 valve was removed from the aircraft and bench tested as outlined above and shown in Figure 2.

Test results indicated that this valve was also malfunctioning and in its worsening condition, the pilot would soon be looking at an “eye-ball” indicator warning of low system pressure on the starboard engine.

A second valve was placed on order.

For instructional purposes, one of the 2H30-16 valves was disassembled with the intent learning the cause of failure.

The valve cover was removed from the valve body along with the diaphragm/disc and spring assembly.Examination of the under side of the assembly showed the disc contaminated with carbon dust with cracks in several places.It was also evident that uneven wear of the disc assembly resulted in the disc not seating completely against the valve inner housing.

Uneven disc wear, cracking and carbon contamination caused this 2H30-16 valve to leak system air pressure at all times regardless of valve adjustment or pump air pressure.
In the field… replacement is the only option.

Going a little further with complete system testing rather than “just fixing the problem” may take a  bit longer but always well worth the effort.

Ken managed to fix the problem, eliminate the developing problem with the 2H30-16 on the starboard engine and prevent additional loss of revenue due to aircraft down time in the near future.

Another one, now in the air,

Ralph Heysek

Aerotech Components, Inc.

Disconnecting the vacuum line from the pump and connecting the test set (following the suggested test procedures), the cockpit gauge showed 5” and the test set gage showed 6”. The gyros appeared to erect normally and it appeared that the system was working normally with the test set connected.

Installing a new vacuum pump did not fix the problem (air pump was bench tested and was putting out 11” Hg.
System works with the CV-700 Test Set, but does not work with the engine driven pump.

Have you run into this problem before?

Regards,
B. J.

During our telephone conversation with Mr. B.J. we talked about the basic system operation and what differences might be taking place between the air pump operation and the Test Kit operation.
His comment confirming that the air pump when bench tested put out 11 Hg. seemed to kick our thoughts into high gear since each CV-700 Test Kit is tested prior to shipment and usually the maximum Hg. created by the Test Kit Ejector is around 14 to 15 Hg. The only thing we could not duplicate is the high air flow from an air pump compared to that generated from a shop air compressor and Test Kit Ejector. The high air flow that is usually generated by the air pump is normally well handled by the aircraft system vacuum regulator in maintaining a desired vacuum setting.
Our next suggestion was to replace the vacuum regulator (with a new or used unit) to see if any change in system operation occurred.

A few days letter Mr. B.J. was kind enough to send us the following information:

As we discussed yesterday, I disassembled the regulator and found that not only was the diaphragm in poor condition but the spring was almost rusted away at the base of the diaphragm. The diaphragm seat was also rusted.

Photos follow:

With a partially rusted and weak adjustment spring the vacuum regulator would allow the diaphragm to rise and bring in ambient air from the engine compartment rather than remain closed and draw air thru the gyro instruments.
A review of proper vacuum regulator operation can be seen at this website under the “sidebar” heading of “DATA SHEETS”.

Thanks to B.J. we now have another answer to a crazy problem!