pressure switch duff?

[shadow]

right just got a new saftey valve for my compressor (says 8.8 bar on it) with an 8 bar 24 liter tank now I filled the tank with water as its the first time I have pressurized it and didn't want to blow myself up I'm using a pair of fridge pumps to do the pumping. anyway pumped up the pressure and the saftey valve opened at about 8.5-9bar according to the gauge so glad that works but why didn't the pressure switch turn them off is it a case of get a new one?

Bit of history I brought a whole 24L 8 bar compressor second hand with a duff pump so I replaced it with a couple of fridge pumps replaced the saftey valve as I broke it while moving the thing around. now I have this problem

out of interest I'd say the tank is good for the pressure or am I wrong. its only going to be used for blowing up tyres and a bit of air dusting and spraying so don't think I need anything with more pressure than this as I'd only be regulating it down to about 60psi at the most and I'm in a home garage in a built up air so really don't want a bomb here

 

[shenion]

You may need to adjust the switch cutoff pressure.

 

[shadow]

how would one do that?
out of interest is there anyone on here in the oxford area who can come and give this project a professional glance over? I've used standard plumbing fittings and ptfe tape to move the drain valve to an accessible place I assume thats okay as I've read its been done here before

 

[rtbcomp]

Open the pressure switch and you should see a big spring with a screw or a nut in the centre. Slacken this screw to reduce the cut-off pressure.

Some switches have two biggish springs with two adjusters, adjust each one by the same amount.

Adjust the switches with some pressure in the tank (don't know why, but it's in the instructions for some switches).

PTFE tape - if the fittings used seal on the threads then tape should be OK, if they seal on seats (ie the nuts only tighten the fitting) then you shouldn't use tape.

 

[shenion]

Take off the cover and there will be an adjustment screw or nut. Usually marked with a + and -.

Post a picture if you are not sure. I find the cutoff pressure needs to "settle" a bit after adjustment so let it run a few times.

 

[shadow]

ah I wondered what that big nut was for. I'll try that out of interest is there a lifespan on these switchs? the label on it says manufactured in 1997 so would it be worth spending a tenner on ebay and getting a new one anyway? sorry for all the questions but this is my first time working with something that could actually blow up most of my stuff is DIY car repairs and electronics I thought I'd give myself a bit of a challenge but I'm beginning to lose confidence in myself to make this thing work.

ps. rbtcomp like your Einstein quote

 

[shadow]

right just taken the top off the switch tried to adjust the screw and noticed the big spring has snapped so I'm guessing its a replacement jobbie. I know the three output ports on the switch are 1/4'' the one on the bottem which attachs to the tank is slightly larger I'm guessing 3/8''? where would be a good place to get one looking on ebay at the moment any recommendations

to rbtcomp yeah the fittings used sealent on the threads I couldn't find anything with which to replace it other than plumbers ptfe tape any idea what they actually use? either way it seems to work well

 

[rtbcomp]

I usually use PTFE tape on tapered threads and Loctite pipe sealant on parallel threads. If what you've done works then leave it.

 

[shadow]

yeah if it ain't broke don't fix it lol

 

[shadow]

right can't see any 4 port pressure switchs with a 3/8'' inlet guess they don't sell them I'll have to get a 1/4'' one and an adapter which costs as much as the flipping switch!

 

[normspanners]

Some of the pressure switches on the bay are a bit c**p they tend to have a large differential.
Good value one are

Good pressure switches are telemecanique XMPE12b2431 1/4 bsp, single phase up to 12 bar 174 psi,best part is they have 1 bar differential, built in compressor head pressure unloader and about £25
3ph version is xmpe12c2131
They do hundreds of different ones I spent ages checking part number /costs, they can be up to £100 for virtually the same just maybe diff thread.
I have one in my hand as I type!
The BIG advantage is the pressure diff. the cheaper chinese ones are at best about 3bar

I posted this for a member last year.