Question

I have a 1979 Beech A36TC with BF Goodrich deice boots installed. After installing your CV1J4 “Clear View”, filter we noticed it getting black only after a few hours of flight. Checking into the system, we found a bad deice timer module. Unable to obtain a module right away and with summer coming we decided to disconnect the boot system after installing a new “Clear View” filter. Now after about 30-40 hours of flying the “Clear View” filter is again getting darker. Looking at your “Data Sheets” on the 2H22 Deice Valve, is it possible that the valve is putting backpressure on the pump even though it is electrically disconnected?
David K.
Utica, IN

Answer

Yes sir Mr. K, you did read the data sheets correct and have located your problem!

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.