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Old 14th Jul 2020, 10:59 am   #1
slidertogrid
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Default What was this used for? Mercoid Control

My mate was having a clear out of his long stored junk.. Sorry! I meant to say quality useful items...
He kindly asked me if there was anything I wanted before he moved it on to storage area "B" (the tip).
Amongst The items was this Mercoid control switch. I had a quick look on google and found out they are used for pressure control, used on compressors and the like. I have seen a lot of air compressors the type used in garages for air tools etc but I have never seen anything like this.
Can anyone enlighten me as to it's lightly application? It looks very well made.
I realise the hazards of Mercury so I will treat it with the respect it deserves.

Rich.
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Last edited by AC/HL; 14th Jul 2020 at 12:08 pm. Reason: OT aside edited
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Old 14th Jul 2020, 5:52 pm   #2
duncanlowe
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Default Re: What was this used for? Mercoid Control

I can see an aneroid tube in it. Therefore presumably as the tube changes shape according to pressure it tilts the mercury switches to start and stop the compressor? Normally the compressor controls you see are integrated with an unloader (the thing that makes the hiss when switching off) so that the motor doesn't try to start under load.
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Old 14th Jul 2020, 6:03 pm   #3
russell_w_b
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Default Re: What was this used for? Mercoid Control

We used to have similar installed on the de-ionised vapour-phase water cooling systems of the Marconi BD272 / B6122 250kW HF transmitters at BBC Skelton. Same idea; different manufacturer. An alarm would be indicated if pressure dropped.
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Old 14th Jul 2020, 9:45 pm   #4
high_vacuum_house
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Smile Re: What was this used for? Mercoid Control

Looks as if there are 2 pointers on the dial so possibly connected to some chemical or air process pipework and to cause an alarm to be indicated at a control panel should the measured pressure deviate outside of its set parameters.

Love the well made construction of the gauge though!!

Christopher Capener
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Old 14th Jul 2020, 9:54 pm   #5
Lucien Nunes
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Default Re: What was this used for? Mercoid Control

That's a very nice pressure switch. The bourdon tube and mercury switch combination can offer lower switching differential and better repeatability than more basic types. Such a switch might be chosen for monitoring or controlling a process, e.g. the pressure in a reaction vessel, rather than just starting a compressor.
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