Pressure switch failure . Relay question

Hi , 

I’m looking for some Advice . 

I keep getting failing pressure switch’s on shuflo pumps . 

Its only happening on one van , the other van is fine and it’s only happened once in years . But the other van it’s happening within hours of replacing a new 16amp switch . The only thing different in the second van is the wiring , it’s not as heavy duty , I basically cut down a decent extension lead and used the wire ( I was in a rush ) could this be the problem ?? 

Also I’m using flow controllers although noting flash just analog . 

Also ive read about using a relay 40amp and the will take the strain off the pressure switch and prevent them from burning out ? If so has anyone got any info on how to wire them up 

Thank you 

Out of interest, what 'not so flash analogue controller' do you have @Klean windows and where is it situated in the circuit; ie. before or after the pressure switch?

spruce said:

Out of interest, what 'not so flash analogue controller' do you have @Klean windows and where is it situated in the circuit; ie. before or after the pressure switch?

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Hi Spruce , thanks for the reply . it’s just a basic controller , internally a motor speed controller with a switch that’s within a waterproof plastic in closure that you just turn up and down by turning the **** , it’s not a well marketed controller with a branded name like that digital ones that you calibrate . It’s wired up as usual ( as the instructions say ) linked to the power and the motor.  I’ve got three of them , two in one van and one in an other , all wired in the same sequence. I’ve never had this problem with the two man van . But the one man van is going through micro switches like I’d go through smarties. 

spruce said:

Out of interest, what 'not so flash analogue controller' do you have @Klean windows and where is it situated in the circuit; ie. before or after the pressure switch?

Click to expand...

Klean windows said:

Hi , 

I’m looking for some Advice . 

I keep getting failing pressure switch’s on shuflo pumps . 

Its only happening on one van , the other van is fine and it’s only happened once in years . But the other van it’s happening within hours of replacing a new 16amp switch . The only thing different in the second van is the wiring , it’s not as heavy duty , I basically cut down a decent extension lead and used the wire ( I was in a rush ) could this be the problem ?? 

Also I’m using flow controllers although noting flash just analog . 

Also ive read about using a relay 40amp and the will take the strain off the pressure switch and prevent them from burning out ? If so has anyone got any info on how to wire them up 

Thank you 

Click to expand...

The correct size of cable to run the pump is very important, especially if distance is involved.

If I was using extension cable wiring, which I have done, then I would be looking at 2.5mm 16 amp cable. You will notice that a 10 amp extension cable uses 1.0mm cable which is really pushing the limit IMHO. But this won't be causing p/s failure.

I'm not going to reinvent the wheel so I'm giving credit to M&C Window Cleaning on another forum for doing these wiring diagrams.

You have to chose the right relay. A 4 pin normally open relay will work fine but you need to chose relay pin 87 with 5 pin and leave pin 87a. I believe you are best to buy a relay with fly lead to make wiring easier. You can use 15 amp strip connectors to join wires.

Thank you spruce . Much appreciated! 

Ive just tried again there , switch got red hot and failed ... ive ordered a new pump so I’ll check if that does the same . If it does I’ll pull it all out and start again and get a relay in . Thanks again. 

Klean windows said:

Thank you spruce . Much appreciated! 

Ive just tried again there , switch got red hot and failed ... ive ordered a new pump so I’ll check if that does the same . If it does I’ll pull it all out and start again and get a relay in . Thanks again. 

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If the switch is getting hot and this pump is going through switches, then it could well point to an issue with the pump drawing too much current. Maybe there is a faulty circuit in one of the armature windings. The 'field' magnets are fixed on the motor housing, but one of those could have 'failed' and moved.

The other issue is of the pressure switch adjustment.screw. If its unscrewed too much and the pressure switch is set too low then its going to cause the pump to cycle. Every time the pump switches on and off it causes stress on the microswitch.

In the early days we had 65psi pumps. We had no end of issues with burnt out pressure switches. Then Shurflo introduced 100psi pumps for window cleaners. The parts were identical to the 65psi so the only change I could see was the pressure switch adjustment. The pressure switches on the 100psi pumps did last longer.

But the 100psi pumps drew more current under those higher pressure demands. So then PWM controllers started to be used and the pressure screw adjustment lowered to reduce battery consumption. This was fine for those who used a low water flow, but if the cleaner had the PWM of full throttle, then the pressure switch was put under stress again.

In our own situation we tried the 3.8lpm pump but this didn't help. Williamson pumps then introduced the first Varistreams and we bought one. We are still using that 3.8lpm pump on the van 12 years later and it still has a disconnected burnt out microswitch in that pump. Those first analogue Varistreams paid for themselves many times over just by what we saved on buying new pressure switches.

Just came across something interesting regards to the microswitches in these pump pressure switches.

Speaking to an electrician, he told me that the 15amp rating printed on the side of these switches is only good for 250v AC not DC (direct current). It’s also different at lower voltage.

For DC, it’s a lot lower. Turns out that for 12v DC the same micro switch is only rated at about 5amps.

So it’s no wonder these micro switches burn out quickly when relied on solely to control our pumps especially if we replace them with 250vac 6amp versions.

Marko067 said:

Just came across something interesting regards to the microswitches in these pump pressure switches.

Speaking to an electrician, he told me that the 15amp rating printed on the side of these switches is only good for 250v AC not DC (direct current). It’s also different at lower voltage.

For DC, it’s a lot lower. Turns out that for 12v DC the same micro switch is only rated at about 5amps.

So it’s no wonder these micro switches burn out quickly when relied on solely to control our pumps especially if we replace them with 250vac 6amp versions.

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Agree, with you that those pressure switches from Maplins weren't up the the correct specification, but we even had problems with the genuine part from Williamson pumps.

Surely 15 amp measured in any voltage is the same load or current. The problem with DC is that the arc or flash made when the contacts make or break is very aggressive. So rating the switch lower for DC would reduce the aggressiveness of the spark and prolong the life of the switch. So in a round about way the electrician is correct.

Whilst most switch failures are the result of the contacts melting away, a few have been where the contacts are welded or fused together.

This is the identical switch supplied in the Shurflo pumps.

https://www.ebay.co.uk/itm/MICROSWITCH-PIN-PLUNGER-SPST-NC-15A-250V-NWK-PN-V-15-2C26-K/272876781521?hash=item3f88b93fd1:g:1CIAAOSwP4ZZ16R6

If the genuine article supplied by the manufacturers isn't up to the job I'm afraid the only real answer is a 30 or 40 amp relay. They are also cheap, available everywhere and more convenient to replace.

To say how long standing this problem is and how cheap the relays are, I’m surprised that they aren’t fitted as standard in modern setups.

As per my knowledge you have to chose the right relay. A 4 pin normally open relay will work fine but you need to chose relay pin 87 with 5 pin and leave pin 87a. I believe you are best to buy a relay with fly lead to make wiring easier. You can use 15 amp strip connectors to join wires.

TimiSchor said:

As per my knowledge you have to chose the right relay. A 4 pin normally open relay will work fine but you need to chose relay pin 87 with 5 pin and leave pin 87a. I believe you are best to buy a relay with fly lead to make wiring easier. You can use 15 amp strip connectors to join wires.

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Most 12v headlight relays work fine as they are rated at 40 amps - in the UK anyway.

https://www.ebay.co.uk/itm/12V-Automotive-Changeover-Relay-40A-5-Pin-with-Socket-Holder/262397418191?epid=1244664374&hash=item3d181adacf:g84AAOSwXXxZVgha:rk:2f:0