Pneumatic mast in a television remote broadcast van - help learning workings

[wb0gaz]

A ham friend has acquired a retired TV remote broadcast van. It seems to be typical for the genre - a pneumatic mast protruding from the roof of the (ford econoline 1980s era) van which can be extended to perhaps 40 feet (and retracted, of course) using compressed air supplied by an AC motor and relatively large DC inverter. The installation was made by a company in Massachusetts some years back; the company is long gone (trail goes cold about 2006) and documentation pertaining to the build is not obtainable.

My task is to learn enough about this type of installation so that I can help bring it back to service (for ham radio usage.) My responsibility area is the mast and it's associated controls and pneumatic air compressor/valve system.

Is there a user community somewhere that could help me identify key components (principally the mast itself) and advise areas of caution/care so that I don't inadvertently damage the installation while I try to get it going again?

Thanks for any pointers, advice, and of course any requests for clarification!

[pcprogrammer]

Maybe posting some pictures of what you are dealing with will help. Pneumatics is not that difficult and who knows what expertise hangs around here on the forum.

[Geoff-AU]

never looked inside a pneumatic mast but it probably works on a similar principle to gas struts

[Andy Chee]

Your biggest issue will be the cylinder seals.  If the business has gone bust, then you might have problems sourcing suitable replacements.  If your cylinder seals leak too much air, the mast won't build/maintain enough air pressure to lift its weight.

[DenzilPenberthy]

I'd bet good money that the seals are standard off-the-shelf types and sizes. Likely to be easily available from a seal supplier if you take the old ones to the trade counter, or measure them yourself.

[CaptDon]

I'll tell you one damned important fact about that mast.....You need a pneumatic switch to KILL the van's ignition if there is any air pressure above about 1 P.S.I. in that mast!!! You also need a valve that REMAINS in the open bleed position for the DOWN function!!! Never close off the bleed when the valve is set to DOWN!! Want to know how many mast sections I had to replace when the 'Talent' drove down the street with the mast still up?? We had one driven into a 13KV 3 phase overhead feeder!! Took out over a city block!! That was no cheap date!! Some of those seals work like a tire pump, they won't let air leak out but will suck in air when the van bounces hard and 'pump up' the mast unless the bleed is in the open position!! I seem to recall ours were 'Wilberts'?

[CaptDon]

Wil-Burt    still in business!!!

[A.Z.]

strange, didn't the mast have a manual "open" valve at bottom to keep it open when not in use ?

otherwise... try lowering it at "sea level" and then driving the van up a mountain...

[wb0gaz]

Thanks for the reply to my posting - this is really in line with what I wanted - practical observations in general. As there is no nameplate or other identification on the mast itself (it's mounted in the van so I may simply not be able position to see  any identifying information), I am at this point just wanting to learn practical tips and tricks, ideally from someone that's used, maintained or installed these things in the past.

Wil-Burt seems to be a current supplier in this space, at least a quick survey of their website alerts me that there are options (such as manual/pneumatic locks and such) to be aware of (I don't know if any of those exist in this unit.) Haven't yet been able find an installer's/operator's guide online anywhere for anything similar, but still looking.

No attempt yet to power on the compressor, as don't yet know which valve is "up" and which is "down" (there is a control system but it's hard-wire logic and not documented). The mast is currently in the nested position (as it was when purchased and transported.) A concern is ensuring that the retraction mechanism is fully understood so it doesn't end up stuck in any other than retracted position. This is definitely a "look before leap" phase!

Photos will of course be helpful but just grappling with how to take useful photos (other than at a distance). The laborious task of tagging each and every wire and air line commences soon.

Again, thanks for the discussion, the contributions here are really appreciated!

[CaptDon]

Things to be aware of, Each of the smaller mast sections (the ones that actually move) will have a small weep hole in the side of the section very close to the top of each section. This has two functions, it will expel trapped rain water when the mast is raised and it is also a good place to squirt in some neatsfoot oil (leather preservative) to lubricate and preserve the seals. There should be flat rubber rings on top of each section to absorb the shock of the collapsing section above. Each section has a 'top cap' that acts as a stabilizing bushing for the next smaller section. The length of the screws that holds the top cap in place is important, if too long they will bind and damage the next smaller section. Also, most systems have a compressor that cuts off at around 50PSI into a storage tank. This pressure MUST be run through a regulator as the mast has a maximum working pressure of something like 10PSI. The mast ALWAYS leaks so the storage tank and regulator act to hold the mast securely in the up position. 'Part way up' is not really an option as the mast will leak down. Compressed air systems need a water drain on the tank which should be bled often and the mast up/down valve is to remain in an open position for down to allow any condensation or rain water leakage inside the mast to have open access for drainage. If the unit is parked outside it is normal for the mast to collect rain water internally. If you pull the sections apart prepare to get dirty and slimey. Best wishes. If the original system seems too convoluted just re-do it from scratch!! Cheers mate!

[wb0gaz]

Thanks, CaptDon - much appreciated.

I envision replacing the control system (no need for NTSC video steering and all that!), and an interim step would be just to operate the thing manually to gain some confidence that the basic mechanism is serviceable.

There is a pressure regulator (and pressure meter) (in the path from compressor output to a pair of valves that might be up/down), but haven't yet traced the air flow.

Not close to an initial manual test yet, still focusing on "learning the ropes."

The hard-wire control system looks like it wasn't left in an operating condition (some plug-in relays missing) so almost certain the whole system is not plug-and-play at this stage.

Thanks again!

Dave

[babysitter]

How about posting a few pictures of the things which are hard to trace?

I would expect

a) two electrical connections to at least one valve to select up and down, or pneumatic switches to do so.
b) electrical or pneumatic switches that detect extended and collapsed state, possibly interlocked.
c) pressure regulators to prevent damage by overpressure
d) possibly everything defaulting to collapsed state, so only active for expansion.


Try to locate those things that look like related to it first. Pneumatics look a lot like electronics.
BR
Hendi

[wb0gaz]

Thank you Hendi,

That is very helpful guidance.

My next work session is in a few days - this will help me concentrate on documenting with photographs.

Dave