Flow switch?

ritelec

ritelec

Senior Member
Location
Jersey
Hi. I haven't wired any controls or motors in a while so I'm researching and reading to see what I will need to wire a pond pump motor.

Back story: New home owners of a house have a pond that was used to supply water to lawn sprinklers. The pump and wiring are in disrepair.

They had someone replace the pump. The new pump is single phase, 2 HP, Thermally protected, 230V, FLA 8.3, SF1.4, SFA12.
The idea, is to have the existing pool timer zone controller (Hunter) which was controlling an old starter relay, instead control a new starter with heaters that I will put in (researching)

Would controlling the 250v starter from the 120v sprinkler control circuit be in violation? ( I will research )

FLOW switch?? ... This pump has a 2" pvc pipe going into the pond to supply the water to the pump and sprinklers. If this pipe gets clogged, there is nothing to turn the motor off from what I can see. Would anyone know of a FLOW SWITCH that I can install in that pipe that would break or make the control circuit if that pipe clogs or the pond drys up??

edit: rethinking this, a flow switch wouldn't necessarily work because the motor would need to be running, or would it? What type of switch would sense if the pipe is empty or clogged?

Thank you.
 
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What you do with a flow switch is to have it Normally Open, held closed by flow, so that if flow stops, it opens the control circuit and drops out the contactor. But to make that work, you need a timer to allow the pump to start first. So you have a timer energized with the contactor that has Normally Closed contacts shunting the control circuit around the N.O. Flow switch, then once the flow switch closes something like 2 seconds later, the timer times out and opens it's contacts, but everything stay running until something else shuts it down.
 
Probably the easiest way is to use a sump pump float switch. When the water level drops too low, it shuts off the pump. Since your pump is 240, the float switch has a 120 volt in/out plug, you would need a 120 volt coil on the motor controller, or cut the end off, and wire it to break one leg.
 
If you add a bladder tank, you can use one of these to shut the pump off if the line gets clogged or pond goes dry. It’s manual reset, but would require no control from the sprinkler system, or running wires to a float control at the pond.
 

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hillbilly1 said:
If you add a bladder tank, you can use one of these to shut the pump off if the line gets clogged or pond goes dry. It’s manual reset, but would require no control from the sprinkler system, or running wires to a float control at the pond.
Click to expand...

I'm trying to understand this. How and where is the bladder tank (expansion tank?) placed ... require no control from the sprinkler system? I see contacts in there but I'm not getting it.
 
ritelec said:
I'm trying to understand this. How and where is the bladder tank (expansion tank?) placed ... require no control from the sprinkler system? I see contacts in there but I'm not getting it.
Click to expand...
Pump is always pressurized, when sprinkler water solenoid is opened, pressure drops, pump starts rebuilding pressure. If no water is available, such as pond being dry, pressure keeps dropping until low pressure cut off is reached, and pump is locked out requiring manual reset. Kinda like hooking the sprinklers up to a city water connection.
 
Ok. That’s where I lost it. From what I see, the pump won’t always be pressurized.

There’s a 2” pvc pipe laying in the middle of the pond connected to the input of the motor. The pump turns on and sucks the water through it feeding to the sprinkler system.
Pump off and I think water will remain in that pipe ( or trickle back into pond ) but I don’t see how it will be pressurized.
 
Thank you for the help. I looked at the foot check valve. The motor is self priming but it looks like a good idea to install this foot valve.

Still the question is once this pipe is full of water how is it pressurized.

Im not a plumber, but would the bladder tank just be placed hanging underneath that feed 2” pvc pipe? Will the weight of the water laying on the bladder make and break the switch and that weight of the water laying on the bladder is “ the pressure”?

Thanks again.
 
ptonsparky said:
You no doubt have an open discharge. That switch isn’t for you.
I would monitor the current of the pump. Under 5 Amps it shuts down after 19 seconds. (Random #s).
Click to expand...
Current switches don't always work well for small motors driving centrifugal pumps to detect low or no flow. Sometimes there is not enough difference in current.
We used these, but they are way too expensive for this project.
 
ptonsparky said:
You no doubt have an open discharge. That switch isn’t for you.
I would monitor the current of the pump. Under 5 Amps it shuts down after 19 seconds. (Random #s).
Click to expand...
If it has a sprinkler control box, it turns the pump on, and opens the zone water solenoid. Thats why the bladder tank must be added for the pressure switch to work properly. If the pump output is lower than the usage, it could work, but if the output is higher, the pump would cycle quickly, eventually burning out the puno.
 
To get desired operation out of the sprinklers you need a minimum water supply pressure.

If sprinkler controller is what starts and stops this then all you really need is a NO pressure switch with a NCTO timer to bypass the pressure switch long enough at startup to allow for the pressure to build. That delay could be a few seconds to a minute or two depending on how long it would take to build pressure. If system is completely empty at startup it could be the minute or two instead of a few seconds. Hand off auto switch could be handy if you ever need to manually run to try to clear problems, prime a pump, etc.
 
I'm glad you mentioned "pressure". As I looked at the motor with a glass pressure gauge sticking out of the side of it, I asked my self whats going to turn this thing off if the pressure becomes to great, then back on when pressure drops, then what good would that be if the sprinkler keep turning on and off as the pump motor turns on and off?
Would they make some type of mechanical pressure relief valve that releases pressure so the pump can keep running, and install a HIGH pressure electrical switch to cut power if the pressure goes past the mechanical high pressure switch setting?
I think adding the suggested foot check valve is a good idea even if the motor is self priming.
 
ritelec said:
I'm trying to understand this. How and where is the bladder tank (expansion tank?) placed ... require no control from the sprinkler system? I see contacts in there but I'm not getting it.
Click to expand...
The system may not have one and you may not need one. The pressure tank would tee into the discharge of the pump and just sit there keeping pressure on the water lines when the pump isn't running. They are most commonly found on domestic well systems were you only need the well pump to come on when someone is taking a shower and not come on when someone is filling one glass of water.
ritelec said:
I'm glad you mentioned "pressure". As I looked at the motor with a glass pressure gauge sticking out of the side of it, I asked my self whats going to turn this thing off if the pressure becomes to great, then back on when pressure drops, then what good would that be if the sprinkler keep turning on and off as the pump motor turns on and off?
Click to expand...
That's what a pressure switch would be for, but you may not need one. For a sprinkler you could simply start the pump every time a sprinkler comes on and shut it off every time the sprinkler stops. Over pressure isn't much of a problem usually. If the sprinklers were clogged the pump was running it would just sit and churn inside the pump. A bigger problem is when the pump is dry and the motor keeps spinning and burns up the seal in the pump.
ritelec said:
Would they make some type of mechanical pressure relief valve that releases pressure so the pump can keep running, and install a HIGH pressure electrical switch to cut power if the pressure goes past the mechanical high pressure switch setting?
Click to expand...
That is what a pressure switch does. It opens when the pressure gets high enough and closes when the pressure gets low enough. As long as there is water high back pressure doesn't hurt the pump, and the motor would be happier with higher pressure than it will be with lower pressure. The pump and motor's job is to move water. More pressure in the lines means the pump has to move less water to keep them full so the motor doesn't need to work as hard.
ritelec said:
I think adding the suggested foot check valve is a good idea even if the motor is self priming.
Click to expand...
It is critical in most cases. Pumps are really, really good at pushing water out, but they are lousy at sucking water in.
 
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