Page 13 - Volume 12 Number 12

The Flow Pack and the Pneumostat
Near the end of another pre-buy inspection, I found a weak flow pack on a King Air and had the same situation – everyone was itching to close the deal and move on. The seller protested vigorously. He said that pack had been changed earlier that year. So, I asked if the pneumostat was changed at the same time and the answer was no. Hmmm.
The flow pack and the pneumostat work together. The pack provides the flow and the pneumostat adjusts the flow rate according to temperature and pressure. The flow pack has orifices that become clogged over time and the pneumostat has bellows that get dirty, decreasing effectiveness. There is no way to test the pneumostat separately unless you have a pneumatic diagnostic bench lying around. In this example, the flow pack was changed and the problem seemed to go away for a while, then it came back because the pneumostat wasn’t up to par.
In all my days of working on King Airs, I learned early to exchange or repair the flow pack and pneu- mostat together, every time. What it saves in time and aggravation is well worth the few hundred bucks spent on an exchange pneumostat. This is a key point with pneumatic flow packs and I cannot stress this strongly enough.
When I had my shop, I knew a pneumatic repair facility that did fantastic work. I sent flow packs with pneumostats to him all the time. He would repair or overhaul them as necessary. I could get exchange units from him if my customer was in a big hurry. He was able to “marry” the pack and the pneumostat, fine tuning them together – a great bonus.
Electronic Flow Packs
Electronic flow packs offer peak performance over a much longer period of time than their pneumatic counterparts. The down side is they are very expensive to exchange and they are only available from Beechcraft (Textron Aviation).
Electronic flow packs have a thermistor instead of a pneumostat, and they have a controller (not the pressurization controller in the pedestal). If your King Air has electronic packs and you find a weak one, there are a couple things your shop can try before exchanging the pack. The thermistor can be ohm’ d out to ensure it is working properly. To troubleshoot the controller, swap it to the other side. There is also a test box available that checks proper operation of the electronic flow pack system.
Pneumatic packs can be changed to electronic; Beech has a kit.
DECEMBER 2018
KING AIR MAGAZINE • 11