Pressure relief valve problem

[Iain_S]

The square D switch is plumbed in to the pressure side of the pipework via a "T" piece. The supply to the pump goes to one side of the switch, and the opposite contact feeds the pump.

I converted one of these pumps a while ago for switched operation, but cant remember all the details. Under the end cover of the pump was a circuit board, and the modification was removing the power feed from the circuit board and connecting it to the connection to one of the motor brushes, basically bypassing the board. If I remember correctly, the negative lead was already connected to one brush, and the positive lead was de-soldered from the electronic gubbins and re-soldered to what was the output from the electronics. 

[Tony Brooks]

13 minutes ago, starman said:

So how would I fit a D Squared switch Tony? From what I can see the mechanicals of mine are the same as a standard one - the difference is at the nose where there is some sort of electrical pick up that links back into the motor and some sort of little nylon jobby (a technical term) that can move up and down. 

There's also a small sealed  box of electric bits called an 'EMI filter' on the 12v feed wiring to the pump. 

Well, I would not fit one to your pump although it may work but would fit one to a "standard" pump.

Normal pumps usually have red and black fly leads so you can connect them to the boat's wiring. The black one usually runs straight into the cylindrical pump body while the red one goes into the pressure switch assembly on the end of the pump. Close by a usually black wire runs form the pressure switch into the cylindrical body, this is the positive pump feed.

 

Disconnect that wire from the pressure switch or even cut it. The boat's positive  pump feed wire runs to one set of contacts on the D Square switch (they are often double pole switches so you can use one or the two contact pairs in parallel). Another new piece of cable runs from the other contact of the pair to the wire you disconnected from the pressure switch in the pump. The pump's internal pressure switch is now out of circuit and the D Square switch controls the motor.

I suspect the EMF filter is used because the speed control on your pump is done by high frequency pulse width modulation so it might cause radio interference via the boat's circuits unless it is suppressed.

The pressure switch is T'd into a convenient point in the plumbing after the pump.

[starman]

19 minutes ago, Tony Brooks said:

Well, I would not fit one to your pump although it may work but would fit one to a "standard" pump.

Normal pumps usually have red and black fly leads so you can connect them to the boat's wiring. The black one usually runs straight into the cylindrical pump body while the red one goes into the pressure switch assembly on the end of the pump. Close by a usually black wire runs form the pressure switch into the cylindrical body, this is the positive pump feed.

 

Disconnect that wire from the pressure switch or even cut it. The boat's positive  pump feed wire runs to one set of contacts on the D Square switch (they are often double pole switches so you can use one or the two contact pairs in parallel). Another new piece of cable runs from the other contact of the pair to the wire you disconnected from the pressure switch in the pump. The pump's internal pressure switch is now out of circuit and the D Square switch controls the motor.

I suspect the EMF filter is used because the speed control on your pump is done by high frequency pulse width modulation so it might cause radio interference via the boat's circuits unless it is suppressed.

The pressure switch is T'd into a convenient point in the plumbing after the pump.

Thanks Tony - sounds simple enough. So a daft follow up question: what does this achieve? Does this turn a standard pump into one like the Sensormax which runs at a constant pressure by revving the motor suitably up and down? Or is it just a more reliable version of the standard pump switch?

As you can see, I'm getting confused!

[MtB]

8 minutes ago, starman said:

Thanks Tony - sounds simple enough. So a daft follow up question: what does this achieve? Does this turn a standard pump into one like the Sensormax which runs at a constant pressure by revving the motor suitably up and down? Or is it just a more reliable version of the standard pump switch?

As you can see, I'm getting confused!

I'm confused too. What does a Square D switch do that the pressure switch on any 'ordinary' pump doesn't?

[rusty69]

3 minutes ago, Mike the Boilerman said:

I'm confused too. What does a Square D switch do that the pressure switch on any 'ordinary' pump doesn't?

It's a lot more robust than the tiny inbuilt micro switches. 

Lasting a lot longer especially if coupled with a relay. 

Edited February 24, 2017 by rusty69

[cereal tiller]

4 minutes ago, Mike the Boilerman said:

I'm confused too. What does a Square D switch do that the pressure switch on any 'ordinary' pump doesn't?

It can be adjusted for CUT IN and CUT OUT Pressures that suit the plumbing layout of a boat,have always used them

And if they trigger a Relay to start the Pump there is no switch failure

Edited February 24, 2017 by cereal tiller

[MtB]

I WANT ONE!

[rusty69]

1 hour ago, Mike the Boilerman said:

I WANT ONE!

Ebay is your friend. There is also a cheaper square d clone on there. 

Item 162380543486

Edited February 24, 2017 by rusty69

[cereal tiller]

1 minute ago, Mike the Boilerman said:

I WANT ONE!

You are still saving up for a Buss Bar!

[rusty69]

Just now, cereal tiller said:

You are still saving up for a Buss Bar!

Na, he was going to make some, thus saving money for a Square D switch. 

[MtB]

You're both wrong. My gf is going to knit me one.

[starman]

44 minutes ago, cereal tiller said:

It can be adjusted for CUT IN and CUT OUT Pressures that suit the plumbing layout of a boat,have always used them

And if they trigger a Relay to start the Pump there is no switch failure

It's starting to go over my head now. How would I know what my cut in and out pressures are - and how would setting them up benefit the system?

I was a fan of the Sensormax until it went wrong - it was very quiet, gave smooth water delivery  and needed no accumulator. It also demanded no tech knowledge from the installer!

[cereal tiller]

1 minute ago, starman said:

It's starting to go over my head now. How would I know what my cut in and out pressures are - and how would setting them up benefit the system?

I was a fan of the Sensormax until it went wrong - it was very quiet, gave smooth water delivery  and needed no accumulator. It also demanded no tech knowledge from the installer!

Something like 7PSI cut in as standard and 20 PSI ish cutout,would likely be OK for most applications but can be adjusted to suit

 

Accumulator means less pump Cycling and smoother flow,a must have

 

 

[Mikexx]

1 hour ago, rusty69 said:

It's a lot more robust than the tiny inbuilt micro switches. 

Lasting a lot longer especially if coupled with a relay. 

Just saw a youtube explanation of the Square D switch of how the on and off pressures can be set. The contacts look meaty with a healthy snap on and off, I'm surprised you would consider a relay? A relay is also another thing to go wrong.

Edited February 24, 2017 by Mikexx

[rusty69]

1 minute ago, Mikexx said:

Just saw a youtube explanation of the Square D switch of how the on and off pressures can be set. The contacts look meaty with a healthy snap on and off, I'm surprised you would consider a relay? A relay is also another thing to go wrong.

Yes a relay may be overkill. The switch is pretty substantial. But a relay only costs pence and if you keep a spare can be swapped out in seconds. 

[WotEver]

10 minutes ago, rusty69 said:

Yes a relay may be overkill. The switch is pretty substantial. But a relay only costs pence and if you keep a spare can be swapped out in seconds. 

Just this. If the contacts were to burn out, as unlikely as that may be, it's the work of just a few seconds to replace the relay. 

[cereal tiller]

15 minutes ago, rusty69 said:

Yes a relay may be overkill. The switch is pretty substantial. But a relay only costs pence and if you keep a spare can be swapped out in seconds. 

The Relay contacts would close faster than a Venerable Spring

[Ex Brummie]

Square D has always been the industry standard for pressure switch applications in fluid applications. When the flimsy unit built into your pump fails, this hardy unit will replace it, and still be effective for years to come. A big advantage is you can set your own parameters to suit your installation.  

[Iain_S]

The contacts on a square D switch are a lot meatier than on the sort of relay that is likely to be used.

[cereal tiller]

6 minutes ago, Iain_S said:

The contacts on a square D switch are a lot meatier than on the sort of relay that is likely to be used.

And they will never Arc if a cheap disposable relay is used,honest

[Tony Brooks]

Proper Square D switches had/have a magnet to help draw the DC arc away from the contacts so apart from the contacts being big meaty ones there will be far less burning. Also as all those I have seen are double pole ones if you wire it using just one contact set in 50 to 100 years when those contacts fail you have another set.

I would definitely use a relay with the inbuilt micro switches but not so fussed with a Square D switch.