Q&A: Vacuum system inspection and maintenance, options for replacing flexible hoses

Written by Steve Ells
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Hi Steve,
I am the proud owner of a 1983 Cessna T210N. My 210 has everything: dual alternators, dual vacuum pumps and full de-icing equipment. It has safely transported me all over the west ever since I bought it seven years ago.

I recently moved my base of operations over 200 miles to a new airport. I followed advice I had read in Cessna Flyer and asked around the airport for advice on a mechanic. The one I selected just finished the inspection part of the annual and he insists that it's time to remove and inspect the vacuum manifold.

From what I can tell, this manifold is located up against the cabin side of the firewall—which means it's going to take a lot of time to get in there, remove it and reinstall it.
I've never used the emergency vacuum system so I'm figuring this manifold is just fine. Do you think I should let him clean it?

—Vacuum Vince

Dear Vince,
My recommendation is to give your entire vacuum system a thorough inspection since your pumps not only drive your artificial horizon and attitude indicator instruments, they also simultaneously provide the pressure and suction necessary for de-icing boot function.
The failure of a pump, or leakage or incomplete operation of one of the one-way check valves in the vacuum manifold during IFR conditions is an extremely serious situation. Every component must work.
The dual engine-mounted pumps are continuously driven by the engine. Each provide vacuum to the vacuum manifold through a regulator. If one pump fails, a check valve in the manifold closes to prevent loss of vacuum out the failed side of the system. In theory, the vacuum manifold is a simple component—but even simple systems need maintenance.

Your T210 is equipped with "dry" vacuum pumps. These pumps consist of a slotted rotor spinning inside an elliptical housing. Carbon vanes slide freely in the slots and are forced out against the housing by centrifugal force. One of the byproducts of operation is carbon dust.
This carbon dust rarely impacts the vacuum side of the vacuum/pressure system, but it can accumulate in the pressure de-icing boot side. (The pressure air from a vacuum pump is vented overboard on non-booted systems.)
Carbon dust is just one of the maintenance items; others that are overlooked by some maintenance shops include changing the instrument system filter and the garter filter at the vacuum regulator.
Finally, the flexible rubber-style hoses between the vacuum pumps, the regulators and the vacuum manifolds need to be changed from time to time. Parker Hannifin (the original supplier of these vacuum manifolds), Aero Accessories (in Service Letter SL-007) and Cirrus Aircraft all state that vacuum manifolds have a 10-year operational life.

Parker Hannifin ceased the manufacture of all its vacuum system components in 2007. Since the supply of new manifolds as well as other vacuum and pressure system components by Parker Hannifin dried up abruptly, companies such as Tempest Plus, Aero Accessories in Gibsonville, N.C., Quality Aircraft Accessories in Tulsa, Okla. and Rapco in Hartland, Wis. have obtained FAA approval to rebuild many of these components.
These companies do their best to maintain a supply of rebuilt products for market. This permits owners to exchange their worn units, but from time to time the lack of rebuildable cores requires that owners send in their components for overhaul.
Check with suppliers to determine if they have an exchange unit available, or budget extra time for shipping and rebuilding your unit.

If you can't find a maintenance log entry or a work order that shows that the vacuum manifold has been checked for operation within the last 10 years, I strongly suggest that you at least include a test and cleaning of the manifold and the replacement of the hoses during this annual. According to Mark Gaulke at Rapco, all hoses should be replaced every six years.
An example of one test procedure for vacuum manifold check valve operation is outlined in an Aero Accessories Service Bulletin. (See Resources for a link to the document. —Ed.) If this test (or another test your mechanic chooses) indicates that the check valves no longer seal, the valves may be dirty or damaged.

When the valve needs replacing, Tempest, Aero Accessories, Quality Aircraft Accessories and Rapco can exchange or overhaul these manifolds. According to Tim Henderson at Aero Accessories, the company is nearing approval for production of new manifolds.
These companies sell through their websites or through aviation parts houses such as Aircraft Spruce and Specialty, Chief Aircraft and others. Exchange prices range from $450 to $850 for the most common ones.
The vacuum pumps and the vacuum manifold are critical components in your T210. Please don't ignore maintenance on this system.

Happy flying.

Hi Steve,
How long do flexible fluid hoses last? I'm referring to the ones with the blue fittings on each end and the black woven outer surface. I started thinking about what would happen if one of these hoses failed, so I looked them all over and they look pretty good.
I have no idea if they have ever been replaced and I'm wondering if it's a good idea to replace all of them on my 1977 Cessna Cardinal RG. I've combed through my logbooks and can't find any entry that notes the replacement of these hoses.

—Wondering William

Dear William,
Good question. You're correct in your assumption that these hoses are widely used in GA airplanes and in your Cardinal RG. Aeroquip and Stratoflex flexible hoses are used throughout the fleet.

I replaced a flexible hose that had been on my 1960 airplane since the day it was pushed out of the factory. Fortunately, it was used in a low-pressure application and wasn't subjected to the heat of the engine compartment.
During my airplane mechanic education I learned that these flex hoses can be built up locally. The procedure is detailed in chapter nine of the FAA document "Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair." This publication is also known as Advisory Circular 43.13-1B, and it's an aircraft mechanic's bible.
In order make hoses, a mandrel is needed. Hose, end fittings, firesleeve and mandrels are available at parts stores.

Many mechanics are reluctant to build up hoses claiming that they don't have a hose testing setup, but all of the commonly used sizes are rated for 3,000 psi. In my opinion there's little chance of a hose leaking if it's assembled properly.
There is one important bit of information that affects certain hoses on Cessna retractable landing gear airplanes like your Cardinal RG. Due to restricted access and the need for a very tight radius on hoses at the gear actuators, Cessna used industrial hoses instead of aviation hoses.

Since the approval for replacing flexible hoses is covered by using parts (hoses, fittings, etc.) that comply with an aviation technical standard order (TSO), for years the only option when replacing these hoses was to buy them directly from Cessna.
Today, one of the easiest and quickest ways to replace all the flexible hoses on your Cardinal is to order a kit from a specialty hose company.

One such company is Precision Hose Technology, Inc. in Tulsa, Okla. Precision quotes around $700 for the seven or eight hoses that are used forward of the firewall, and around $150 for a set of landing gear hoses.
There are other hose suppliers, too. For example, Aircraft Spruce and Specialty will build replacement hoses to dimensions you fill out on an order sheet.
A loose rule of thumb for hose replacement times is at engine overhaul or 10 years, whichever comes first.

Happy flying.

Know your FAR/AIM and check with your mechanic before starting any work.

Steve Ells has been an A&P/IA for 43 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He's a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and lives in Paso Robles, Calif. with his wife Audrey. Send questions and comments to .
Resources
Vacuum manifolds and other vacuum
and pressure system components
– CFA supporters
Aircraft Spruce & Specialty Co.
aircraftspruce.com

Chief Aircraft, Inc.
chiefaircraft.com

Tempest Plus
tempestplus.com

Other sources for manifolds and other vacuum and pressure system components

Aero Accessories, Inc.
aeroaccessories.com

Quality Aircraft Accessories, Inc.
qaa.com

Rapco, Inc.
rapcoinc.com

Vacuum manifold inspection procedure
Aero Accessories' Service Letter SL-007
CessnaFlyer.org/AA-SL007

Flexible hoses
Precision Hose Technology, Inc.
aircrafthose.com

Further reading
Advisory Circular 43.13-1B
"Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair"
CessnaFlyer.org/AC43131B

 

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