High\Low pressure and temperature switches

[Bricklayer]

I have been unable to find a supplier that carries all 3 of these items. I've been into a couple plumbing supply stores and they try to sell me the well pump on at a certain pressure off at a certain pressure. I try to tell them I need a high pressure cutoff switch and a low pressure cutoff switch. It's getting pretty frustrating. Haven't even asked them about the temperature cut off switch that I want to install on it. Where are you guys getting these switches. I've would likely them to be adjustable to some degree so I can set them to where I need them

[arcticair]

If you have an a/c refrigeration shop around you they will be able to set you up with switches , pressure switches can be expensive with a cut in and cut out pressure . They also have a simple disc switch type wich is inexpensive. I am quite sure if you tell what you are doing and the switches are for liquid they will be able to help ( some heads scratching on the counter guys part , but he will understand LOL )

[wiam]

I have added low pressure cut out using a standard 20-40 well pump switch. But this was on an old memtek that had a control circuit so it was easy to add. Are you working on a homemade unit? My current Seprotech I added high temp shut down using a pid. Same deal I added it to the control circuit already there. If this is a homemade unit you will probably need to add relays to control higher amperage than most pid's will handle.

[Bricklayer]

I'm modifying a commercial RO. It's got features on it that I don't really need like auto flush timers and timers for the pump cycle. I'm trying to symplifie the electronics so I can fix it during the sugar season if something goes wrong. It has a low pressure switch but it's tied into a 24 v relay that activates solonoid valves and so on. And it has a flush feature that opens fully the recirc valve during operation and flushes the membrane with concentrate at low pressure during operation. I want to get rid of that also. Basically redo the electronics on this system.

[Tweegs]

See if one of these will help you out:

http://www.dwyer-inst.com/Product/Pressure/SinglePressure/Switches/SeriesA1PS-A1VS#ordering

They have a vid that explains use and the "Dead zones".

[Clinkis]

See if one of these will help you out:

http://www.dwyer-inst.com/Product/Pressure/SinglePressure/Switches/SeriesA1PS-A1VS#ordering

They have a vid that explains use and the "Dead zones".

These are the ones I used on mine for high pressure. Need to wire everything into a simple contactor latching switch. For low pressure just used a 20/40 well pump pressure switch. Works great

[Bricklayer]

Just watched the video. Do these switches automatically reset or do you have to manually reset them. My pump already has a contractor switch. Do I need another one for the high and low switches or can they control the same contactor. I would assume they just break the power to the contactor so the power runs through these switches and then to the contactor for the pump. If one of the pressure switches activates it cuts the power.

[Clinkis]

The high pressure switch resets on its own. You wire the switch to the coil feed for the contractor. If pressure switch activates it kills power to coil, opening contractor and shutting down system.

[Bricklayer]

Does any body have or know where I can find a simple wiring schematic for a setup with a 110 power supply, a hp pump on switch, 30 amp pump contactor switch and low and high pressure switches. I looked at all RO build threads and none had any wiring schematics. I don't understand the whole normally open and normally closed feature on the pressure switches. And if they automatically reset does the pump cone back in or stay off?

[Tweegs]

When talking Normally open (NO) and Normally closed (NC) contacts, there is always a third connection labeled Common (C).
When the device is at rest (take it out of circuit and lay it on your table) a connection is made between Normally Closed and Common. When the device is activated that connection is made between the Normally Open and Common. “Normally” refers to the state the contacts are when at rest with respect to “Common”.

If you use the A1PS-44 from my earlier post, it can be used for both High and Low pressure cut-off in the circuit you asked for (you didn’t stipulate a low pressure pump, so I didn’t include it in the schematic). You can adjust the operating range of the pressure switch so that the circuit breaks when either there is too little or too much pressure. Both cases, in this schematic, will turn the pump off.

In this schematic, the start button is a momentary switch. It will energize the contactor while the switch is held. Once operating pressure is achieved, the A1PS-44 will close its contacts and latch the contactor until any of three conditions occur:
1. Pressure is too low.
2. Pressure is too high.
3. Main power is removed.


I’d suggest at least 12 awg wire and make sure your switches are rated at least 200% of the current listed on the motor spec plate.

14267

[Bricklayer]

I did not mention a low pressure pump your right. I should have. is the high pressure switch wired NC? Can the same switches control both pumps? Or would you need 2 more switches?

[lpakiz]

Just another small detail on NC/NO switches.
At rest, the common and the NC are connected, but the NO is not.
When the switch is energized, the NC opens from the Common and the NO closes.
So, in effect, they simply swap functions. This also serves to make one switch universal. If you need C and NO, you have it. If you need C and NC, you have that option also.

[Tweegs]

14285

OK, here’s what I came up with.

This system uses two relays, two contactors and the pressure switches to monitor the system for high or low pressure conditions.
It should be noted that this circuit was designed specifically for the Dwyer A1PS-44 High pressure cut-off switch. Other switches may be used, but they must operate in the exact same fashion.

As a side note, I’d wire your pumps for 220V if possible. They’ll start easier, run better and a little cooler if you do.

Circuit description:
The main power switch provides power for the entire circuit.
Pressing the LP Start switch will energize relay K2. Once energized, K2 will self-latch, arm the low pressure switch and provide power to the LP pump contactor which turns on the LP pump.
If using a standard Low pressure switch such as the Square D (http://www.homedepot.com/p/Square-D-30-50-psi-Pumptrol-Pressure-Switch-FSG2J21CP/100199433) the switch will activate immediately providing power to the high pressure Start switch. If using the Dwyer A1PS-24/34 pressure switch (http://www.dwyer-inst.com/Product/Pressure/SinglePressure/Switches/SeriesA1PS-A1VS#ordering) the high pressure Start button receives power only after the minimum pressure is reached.

When minimum pressure is achieved on the high pressure side, the high pressure switch will activate. This activation will energize relay K1. Power for both pumps is now maintained through K1, and K2 will de-energize which will prevent an unintended restart during a fault condition.

Fault detection:
Prior to achieving minimum system pressure on the high pressure side, the low pressure switch controls power to the high pressure pump. Any problems with developing low pressure will prevent the high pressure pump from starting. Once minimum system pressure is obtained, both the high and low pressure switches are in series providing a latch to K1. Either a too high or too low pressure event will de-latch K1 and shut the system down.

Pressure switch settings and considerations:
Both pressure switches have minimum and maximum settings.
If using the Dwyer Low pressure switch, the switch minimum should be set to about 5 psi below system running pressure as measured on the low pressure side with the high pressure pump running and needle valve fully open. If using the Square D type, minimum pressure setting can be ignored.
The maximum setting for either switch type must be set higher than the maximum pressure the low pressure pump can obtain. When selecting a low pressure switch, check the specifications on the pump you are using to determine its maximum pressure.

The high pressure switch minimum should be set as low as possible. Hopefully this is low enough to activate with the needle valve fully open. The maximum, or cut-off value, is set to your preference.

Design limitations:
This design is very basic to keep costs down. As a result, there are a couple of minor things I did not address.

First- At main power turn on there is a small chance that the high pressure pump may briefly start. It shouldn’t last more than 1/100th of a second though and shouldn’t cause any damage.

Second- If the high pressure switch minimum setting can’t be set low enough, you’ll need to stand there and hold the high pressure start switch while closing the needle valve until you have enough system pressure to activate the switch. The “High Pressure” lamp will tell you when you can let go.

Third- As the high pressure switch activates relay K1 will energize. There will be a very brief moment when power will be lost to both pump contactors so you may hear a slight dip in pump RPM as K1 and K2 change states. Again, this should only last about 1/100th of a second.

Fourth- Electromagnetic Interference (EMI). There’s a lot of arcing and sparking going on as relays and contactors open and close, magnetic fields are generated as the coils of these devices are powered and de-powered. These actions cause spikes and potential operational interference in the form of what we call transients. If this were a digital circuit, prevention/suppression of transients would be mandatory. Generally speaking, relays and contactors aren’t usually susceptible to this type of interference and transient suppression isn’t needed for this circuit. More to the point, however, is that these transients will propagate throughout the AC lines in your shack, meaning that other devices, like your smart phone or laptop (if plugged in and charging), may exhibit some strange behavior. Charging power supplies for your electronics, if of good quality, can normally handle these transients, but best to leave these type of devices unplugged while the RO is running. Additionally, that digital alarm clock you’ve got plugged in out there is probably going to give you the ole stink-eye every time you fire that RO up.

Parts:

Relays- The relays, at a minimum, need to have a 110V coil and the contacts should be rated for at least 5 amps. Any meeting those requirements are fine, but I prefer DIN mount such as these:
http://www.ebay.com/itm/JQX-13F-110-120VAC-Coil-DPDT-8-Pins-Electromagnetic-Power-Relay-w-DYF08A-Socket-/271344249983?hash=item3f2d60ac7f:g:ku0AAOSwjVVVifJ x
The DIN mount makes mounting and wiring easier and much cleaner.
Of course, if using the DIN mount, you’ll need the rail:
http://www.ebay.com/itm/NEW-DIN-RAIL-12-LONG-STEEL-CHROMATED-PHOENIX-CONTACT-0801733-NS35-7-5-/221130534662?hash=item337c682f06:g:keIAAMXQCgpRuz8 o


Contactors- contactors need to have a 110V coil and the contacts should be rated for 2x the rated current on the motor. You can use the DIN rail mount if you like, but contactors are easy to mount and DIN rail isn’t necessary.

Start buttons- I used these:
http://www.ebay.com/itm/Push-Button-Momentary-Press-Switch-Heavy-Duty-Power-NEW-/180637854438?hash=item2a0edaeae6:m:mGjEPuLZCJg82Xp 4eS30Ovw
They’re big and easy to use, but use whatever you want as long as they are momentary and rated for at least 1 amp.

Good luck!

[Bricklayer]

Thanks Tweegs, I'm just waiting for a couple parts to come in and I will be wiring this pump control circuit up. Was just wondering if something like this temperature switch could be used to shut down the system in high temp situation. I could just wire it inline the main power to the circuit before the relays. Then it just cuts power off to the relays shutting the pumps down. Seems like it would http://www.ebay.com/itm/0-120-Degree-Celsius-ENC-ENO-Temperature-Controll-Switch-Thermostat-250V-20A/321520414788?_trksid=p2045573.c100033.m2042&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D2% 26asc%3D36690%26meid%3D1f7af636f5544e98a73ac4b0b90 fbba9%26pid%3D100033%26rk%3D3%26rkt%3D4%26sd%3D231 089237350.

[Bricklayer]

Just trying to wrap my head around the operation of the pressure switches.http://www.dwyer-inst.com/Product/Pressure/SinglePressure/Switches/SeriesA1PS-A1VS#ordering I ordered the 100-500 high pressure switch. Have it set at 250 psi. And the low pressure switch is the 3-40 set at 25 psi. The way I understand it. Is. Both switches are in the normally closed position at rest. The way I think they work is. The low pressure switch is NC untill at least untill pressure is applied. Then it opens to NO on pressure. If I have it set at 25 psi the switch will go to the c position is the pressure falls below 25. ?

The high pressure switch is usually in the NC position at rest with no pressure. And if I have it set at 250 it will move into the NO position on pressure above 250 psi? Am I right?

I found this video on the same switch but different manufacturer showing how it works
http://youtu.be/gC2Hx7n7KY4

[Greensprings sugar]

Any suggestions what contactors to use with this setup! Interested in putting hi/low switches on ro build

[Bricklayer]

I used 2 of these for the pumps. https://www.zorocanada.com/i/G0559002/?KW2&gclid=CPuc6ZLMoM0CFZSCaQod8v4E8g&gclsrc=aw.ds

[Greensprings sugar]

Thanks bricklayer, is your setup close to tweeks diagram? Any problems with hp pump running before relay closes? Any problems with dwyer pressure switches? Trying to figure this out before purchasing a bunch of stuff.

[bowhunter]

These switches have a normally open contact and a normally closed contact. The normally close contact is closed until the pressure reaches the set point. The normally open contact closes when the pressure reaches the set point. For the low pressure switch use the normally open contact so that the pressure pump will not run until the minimum pressure is reached. On the high pressure switch use the normally closed contact so that it opens when the set pressure is reached. So the switches are wired in series going through the normally open contact on the low pressure switch and the normally closed contact on the high pressure switch. The low pressure switch should be plumbed into the pressure pump suction piping and the high pressure switch plumber into the pressure pump discharge unless you're not using a feed pump. In that case the low pressure switch is also plumbed into the pressure pump discharge, but you add a bypass switch around the low pressure normally open contact on the low pressure switch so you can start the pump and then open the bypass switch once the minimum pressure is met and the low pressure switch normally open contact closes.

[Bricklayer]

Haven't fully got it done yet. Little bit of wiring to do. I changed a couple things.
And added 1 more relay to make the hp start switch a latching contact so that if pressure climbs or pressure drops only for a split second it ****s the system down and reverts back to the start up routine. And I figured that to keep the relays powered when they switch over to K1 maintaining power that it's easiest to just hold down the lp start momentary switch until both pumps are going. Keeps contactor from going off then on again really fast on lp pump. I was going to put a solid state off timer on it and set it to 5 seconds but it got complicated from there. So I scrapped that idea. Pushing 2 buttons at same time on startup isn't a big deal.

I'm sure the whole control circuit could of been done with no relays. But I studied the diagram from Tweegs for so long that I actually understand how it works. So I went with it.
I am going to try to finish it up by the weekend and I can try to draw out how I wired it up
Can't really try it out till I get my membrane and lp pump though.
You should have no problem with the Dwyer switches. They are very well made

[Bricklayer]

Tried the control circuit out last night with a few changes and its works great.
Things I changed/added

- Installed a 5 amp fuse between main power and POWER ON switch
- On HP switch changed the wiring to the NC position
- Added a main power indicator Light
- Change location of momentary switch to after hp switch to latching relay with momentary switch ( this provides a fall- out in case high or low pressure is reached. So system will revert back to Ready to start function.
- Installed NC latching mushroom push button kill switch on main power before fuse. Basically a main kill switch
- installed a low pressure bypass switch ( might install a hp bypass switch as well) basically I ran the common wire going to the switch to a NC/ NO selector switch. NC is common from the relay to common on the switch ( auto mode)
Manual mode with low pressure bypassed is commons wired to the NO position on switch then wired to the hp switch

Started the system up a few times last night.

Press start button LP pump starts when enough pressure to activate lp switch is reached.( I have it set to 30 psi) , the hp circuit receives power.
Lp start momentary switch must be held in at same time as the hp pump momentary switch is pressed to activate hp pump
I though this would be a problem but it's actually a good fail safe. It gives you time to let system fill and get air out if need be and if someone tries to use system that dosnt know how. It will shut down as soon as the hp button is pressed

To shut system down the kill button is pressed or I might install and off button for hp pump. If I did one for both and was in bypass mode the hp pump would continue to run and the lp pump would be off. Not good