Two pressure switch boxes on pressure pump installation?

[Aaron Shrogman]

In the attached picture you will see two apparent pressure switches installed in line (one black/one gray). This is the pressure tank/pump installation that pressurizes my house. It is not our well. Our well has a submersible pump that sends water to a 2500 gallon holding tank that then sends water to the installations pictured which has the gray 40/60 pressure switch which pressurizes the well tank shown and ultimately the house. But I am confused why I have two apparent pressure switches here (black/gray). Most installations I have seen only have the one gray 40/60 pressure switch.

 

[Valveman]

I am guessing one of them, probably the grey one, is reverse acting and being used as a low pressure safety. What do you have to do to get the pump started after turning it off and letting all the pressure out?

 

[Sponsor]

 

[Bannerman]

Where is the pipe connected to that is supplying pressure to the switch with the Black cover?

 

[Aaron Shrogman]

The pressure pipe is underneath the gray pressure switch box and comes straight up so you cannot see it from the picture’s angle. In answer to Valveman’s question ... there is gravity flow from the 2500 gallon water tank which is 40 + feet above the location of this pressure tank installation; so when I service this unit I shut the water off during work then once the water shut off is opened, gravity takes the water down through the pressure switches. That usually gives us approximately 20 psi and I simply hold down the throw lever on the black switch (first in line from power source) and the gray switch will kick the pump on and all is back to normal. I power washed my house 2 days ago and must have taxed the switches as the gray one would not engage the four point switch contact to start pump. I then tapped on top of the gray switch cover and it started. Then I opened up the gray switch cover and cleaned it out and now it’s working fine cycling between 40/60 psi. However, based on that temporary failure I wish to purchase a new pressure switch to have on hand in case of a future switch failure. Before doing so I’m trying to understand what the function is of the black switch box. The gray one clearly cycles the pump on between 40/60 psi based on my experience this week. But the start/run lever for the switch is on the black box. I will attach a picture here of the inside of the gray pressure switch with the cover removed during cleaning. Thanks everyone ...

 

[LLigetfa]

I suspect it is just a valveman said, a reverse pressure switch meant to shut the pump off if the pressure drops too low. The lever on the side is meant to override it so the pressure can rise above the threshold.

 

[Aaron Shrogman]

Thank you ... so if the black switch is a reverse pressure switch, which as far as I can tell is functioning correctly, then I could simply replace the Square D 40/60 220v gray pressure switch by rewiring it the same as the existing one and leave the low pressure switch as is, and it should work well?
Pumptrol Pressure Swtch, 40/60 psi, Stndrd, 1/4"FNPS

• Pressure Switch Differential: 15 to 30 psi
• Temp. Range: -22 Degrees to 257 Degrees F
• HP @ 3 Phase - 240V: 3 hp

Please explain to me what the Pressure Switch differential is and why a 40/60 pressure switch has a 15 to 30 psi pressure differential. Thank you ...

 

[Reach4]

Please explain to me what the Pressure Switch differential is and why a 40/60 pressure switch has a 15 to 30 psi pressure differential. Thank you ...

A switch purchased as a 40/60 switch initially comes set up for a 20 psi differential, but that differential can be increased by turning the nut on the small spring clockwise.

 

[Aaron Shrogman]

Thank you for the explanation. How can I test that the reverse low pressure switch is functioning properly as well. Would I just turn off power to shut off pump, drain water from the system, then open water back into system and turn the power back on. If the reverse low pressure switch is working it will not allow 40/60 pressure switch to turn on pump until I throw the lever on the reverse low pressure switch and hold down until pressure is above the low pressure psi (40 psi) on the 40/60 pressure switch? I appreciate all the assistance I have received here over the past three years. Thank you all.

 

[Reach4]

Normally when you don't want a pressure pump to come on when the tank is empty, you would put a float switch in the pressure tank to detect that condition.

If the tank is high enough, I could see a low-pressure reverse pressure switch monitoring the pressure on the input of the pressure pump being useful, rather than having to wire up a float switch. I am not sure why a lockout would be needed. Is the black pressure switch looking at the pipe coming from the tank? Tell us what the two pressure switches are monitoring, or did you do that already?

If both switches are monitoring the pressure out of the pump, I could see the locking reverse pressure switch to serve as an over-pressure device to shut things down if the pump deadheads.

 

[Aaron Shrogman]

Thank you ... and no we haven’t discussed some of your questions yet. To explain, I have a submersible pump in my water well that supplies water about 200 feet horizontal and a climb of approximately 40+ feet to a 2500 gallon holding tank. That tank is full all the time and is monitored by a float valve in the tank. I assume that when the float valve closes, which stops the water from entering into the top of tank from actual well, the back pressure is detected and the submersible pump hits psi limit and shuts the submersible pump off. That 2500 gal. tank then supplies water to the pressure pump installation via gravity which then uses the above ground pump and pressure tank to maintain water pressure in the house between 40/60 psi. This second pump installation is what I have photographed with the two pressure switches. Based on what you shared, I suspect that reverse low pressure switch is installed in line BEFORE the 40/60 pressure switch as a safety so that if the water tank runs dry for some reason this second pump won’t continue to pump or short cycle and burn out. Does that sound logical? Sorry, what did you mean by the expression ‘deadheads’. When I bought this property I was looking for a low water alarm that might alert me to a falling water level in the water tank to address before all the water is gone from tank, but there is none and possibly that is not a common component of a well system. I’m a building contractor but had no well experience until I purchased this property. Thank you for your assistance it is appreciated ... Aaron

 

[Reach4]

Based on what you shared, I suspect that reverse low pressure switch is installed in line BEFORE the 40/60 pressure switch

Before the 40/60 pressure switch? I think you mean before the pressure pump.

When the water inputs of two pressure switches area connected together with pipes, the order of the water connections don't matter. Each pressure switch would see the same pressure on their respective internal diaphragms.

Regarding deadhead, suppose the output of the pressure pump was blocked, and the 40/60 pressure switch failed to turn off the power to that pump. We would say that pump would be dead headed-- trying to pump, but there is no flow of water.

 

[Aaron Shrogman]

Thank you so much for the explanation. And yes ... it is before the pressure pump. So for the first pressure switch to be a low pressure switch is it basically identical in construction as the 40/60 switch but with the psi setting set in such a way that once pressure drops below a certain psi it shuts the pump off completely. Therefore, it’s called a REVERSE low pressure switch because it’s the low setting for psi that actually shuts off the pump instead of the high psi setting that typically provides that function? Is it purchased with those settings preset or is it set by using the psi differential available when it is purchased? I ask that as it is likely I may need to replace that switch as well. Is there a way to determine the psi settings on an old existing switch already in place ... other than just observing when it switches on and off? If these seem like odd questions, please chock them up to my lack of experience with well specifics. Thanks ...

 

[Reach4]

Is there a way to determine the psi settings on an old existing switch already in place ... other than just observing when it switches on and off?

Not the current settings, but the original settings and model could be informative. Lift the black cover, and look inside the cover to see if there is model info.

 

[LLigetfa]

The reverse pressure switch should be set considerably lower than the 40 PSI pump cut-in setting otherwise you may get nuisance tripping. I would set it to 10 or 20 PSI. If you set it a little lower than the static head from the upstream tank, you shouldn't get any nuisance tripping but it will trip if that tank runs dry.

That said, low pressure cutoff by that means is not foolproof. If the pump were to lose prime at about the time water use stops, the pressure will not drop below the cutoff yet the pump can overheat. It is much better to control it via a low level float switch or a current sensing pump saver.

 

[Reach4]

That said, low pressure cutoff by that means is not foolproof. If the pump were to lose prime at about the time water use stops, the pressure will not drop below the cutoff yet the pump can overheat.

If there is water pressure coming down from the tank, wouldn't that be enough to re-prime the pressure pump?

 

[LLigetfa]

If there is water pressure coming down from the tank, wouldn't that be enough to re-prime the pressure pump?

Not if there is no water consumption to purge/move forward the air and/or steam. Even submersible pumps can lose prime.

 

[Aaron Shrogman]

Thank you Reach 4 for suggestions about checking model # of black switch. Will do. I’ve never needed to prime that pump after shutting off water from tank. Gravity brings it down once water service from tank is reopened. I don’t even think I needed to throw the lever to ‘start’ position on low pressure switch when I replaced the pressure tank there two years ago although I’m not sure, can’t recall? It essentially primed itself through gravity feed with a static head pressure sufficient to surpass whatever the low psi setting is on the reverse switch (I’m guessing). I think if the main submersible well went dry and stopped filling tank, or if the water line from tank to pressurizing pump was damaged through trauma or if it became so clogged with corrosion, in those scenarios, the low pressure shut off switch would prove useful. Thank you Lligetfa for your input. All very useful to help me understand the system. Appreciated ...

 

[Aaron Shrogman]

Didn’t see Llegetfa’s last post, must have just come in. That’s a good point about air in system preventing water flow in line and not allowing pump to self prime. I might have been clever enough to keep the line open down line to allow water flow, or the pressure tank may have maintained pressure (if that’s possible) during tank replacement which was pretty quick. Again ... thanks everyone ...

 

[Valveman]

You really don't need two pressure switches. A single low pressure cut off switch will do both, start/stop the pump at 40/60, and shut the pump off if the pressure gets down to 30 PSI or so. If there is enough gravity to keep the pressure above 30 PSI, you don't even have to hold the lever on the low pressure switch to start the pump. As LL says there are occasions when a low pressure cut off switch will not protect the pump from running dry. A dry well protector using amps instead of pressure like a Cycle Sensor is much more dependable, and you don't have to hold the lever to restart the pump after a power outage.

 

[Aaron Shrogman]

Thank you all for your time and information ...