Differential pressure switch testing them?

[moondawn]

hi all

could anyone tell me the best way of testing these if you think one may be acting faulty.

i know they have the two tubes one for example on one side of a fan and one on the other side. from removing the tubes from the switch. My question is should the tube before the fan be sucking and the tube after the fan be blowing/

i was trying to test one on site today but unsure?

cheers lee

[Brian_UK]

[quote=moondawn;206455 My question is should the tube before the fan be sucking and the tube after the fan be blowing?[/quote]
That's correct.

I normally check that the switch is making/breaking by using a length of tube on one port and suck/blow on the tube. Either use a meter across the contacts and/or listen for the switch changing over.

[moondawn]

Hi Brian thanks for the response.

The Switch i was testing was clearing sucking on the ducting before the fan however it only made a contact when i blew through the tube. can anyone explain why that would be?

cheers lee

[B G Scott]

Hi Brian thanks for the response.

The Switch i was testing was clearing sucking on the ducting before the fan however it only made a contact when i blew through the tube. can anyone explain why that would be?

cheers lee

Differential pressure is the answer, now what was the question?

[moondawn]

Differential pressure is the answer, now what was the question?

hi there my question was i was looking at one of pressure these switches on a job to check it over. I withdrew the tubing from the ducting which was before the fan arrows facing towards the fan on the plastic mounting on the duct. once it was withdrew i put a piece of paper on the plastic mounting and observed it was sucking.

i then sucked down the tube which was connected to the pressure switch and no contact made.
I then blew down it and the contact made
I would of thought that it would make when i sucked but this was not the case... Why????

cheers lee

[Brian_UK]

Tubing on the wrong port of the switch or did you have the other tube still connected to the fan discharge side?

[NoNickName]

No, not wrong. If the switch is measuring clogged filter, then it shall switch on high differential, that's correct.
But, it also depends on the microprocessor logic (normally open or normally closed contacts) make or break alarm.

[Magoo]

Try a magnehelic gauge in each circuit to read the pa readings.

[moondawn]

brian : Yes when the side i was sucking the other side of the tubing was connected, so what your saying is i should disconnect both tubes. apply a tube to before the fan side (negative) and suck if it makes contact its good, then apply tube to after the fan (positive) side and blow. if it makes its good.??

no nickname: it depends on the pressure differential switch whether its open or closed switch?

magoo: just looking for a simple test to do on site with the switch to check it works okay.

thanks all

[NoNickName]

no nickname: it depends on the pressure differential switch whether its open or closed switch?

These days, those switches have both NO and NC contacts.