Pressure drop alarm

[mikthebik]

Hi all,

I'm a Computer Engineer with a small farm and I'm kinda butting in here to see if there's a way to check for water supply line breaks.

Do any of you know of any vendor making a pressure drop alarm that would be suitable for monitoring pressure drops in a water supply line?
I've an agricultural line that normally runs at 120 psi. We've had several fitting separations lately, causing significant water loss.
It appears that electrical pressure transducers are ideal for the measurement part, but I've been unable to find a system that uses them for the purpose of reporting significant pressure drops in a supply line.

Thanks much,
Mike Corcoran
Corcoran Ranch
Ramona, CA
MikeCorcoran@CorcoranRanch.com

 

[roydm]

Mike, wouldn't you be better off using a pressure switch, you can use the contact to power up a horn or light.
If you only want it active when the pump is running power it from the pump circuit.
Regards
Roy

 

[mikthebik]

Roy,

There is no pump, I'm on water district ag water. I'm a newbie to this whole area, so was looking for an off the shelf solution. Not familiar with pressure switches, but after a bit of googling and looking at Graingers, it appears to me that pressure switches are probably designed to turn on a pump once pressure drops below a certain pressure. The ones I see have a pressure differential range of 20-30 psi. When I turn on irrigation, I'm guessing I would experience that much of a drop, for a bit. If a break occurs, the drop would be from normal static 120 psi to probably less than 30, so if I used any of the switches I see, I'd set off a signal whenever I turned on irrigation. Do you know of any switches out there that have a differential of something like 80-100 psi? This is assuming I actually understand how the diff switches work.

Thanks much,
Mike C.

 

[BobM3]

Are you thinking just one transducer that measures a pressure or two transducers, a distance apart, that would indicate a delta-pressure (signaling flow)? Using just one would make the alarm sensitive to the supply side pressure. Two transducers would need their wiring to come together somewhere which may be a hassle if they are located a ways apart.

A flow meter instead of pressure transducers may be a better choice. You would need to figure out how small a flow you would want to sense.

 

[HSWSac]

Those switches at grainger would be just the ticket for you. If you got a 40-60 PSI switch, it would turn ON when the pressure drops below 40 PSI, and back OFF when the pressure gets back up to 60 PSI and above. Usually you can adjust those set points. You want a range like that, so that when it drops low, you still know there was a problem until it gets back up high enough again. I'd install a gauge, too, if you don't already have one.


I looked at Grainger's switches and they appear to have many with different factory presets and ranges.

http://www.grainger.com/Grainger/ww...alValue=pressure+switch&L1=Pressure+Switches,

 

[JLSeagull]

Check the current requirements for your electrical load. You probably need a relay to pickup or drop any real electrical load using the pressure switch to activate the relay. Motors etc. are inductive loads. Even the nameplate ratings may exclude inductive loads.

 

[roydm]

As HSWSac says the 40-50 psi switch should work fine, when you have the irrigation on increase the setting until the alarm comes on then back it off until the alarm goes off with a bit more for luck. As he says a gauge would be a wise investment.
I assume when your fittings seperate you get zero pressure i.e. loose all or most of the water.
Most pressure switches are good for 5 amps or so, enough for an alarm of some sort either line powered or if it's remote you could power up a car horn from a motorcycle battery.
Roy

 

[danw2]

considerations:

Pump Switches have wide differentials compared to 'regular' pressure switches, but the differential range generally maxes out at 30 psi.

These pump control switches are all diaphragm activated switches. The specs for Grainger's 60-80 psi pump switch are posted below. Note the max pressure at 100 psi. Although it is burst pressure rated to 300 psi, the switch's repeatability, life and reliability is exceeded at pressures above the rated pressure.

Statement from Square D's specs (who makes similar, if not identical style switches):
During the normal operating cycle, system pressure should never exceed the upper limit of the range when using a diaphragm actuated switch. This will greatly reduce the life of the diaphragm. (pg 6)

http://www.firequip.com.au/files/Te...Controls/Square_D_Pressure_Switch_9013FSG.pdf

con't:
Maximum allowable pressure is the pressure to which a switch can be subjected without causing a change in operating characteristics, shift in settings, or damage to the device.

Pressure surges may occur in a system during the start up of a machine or from valve operation. Surges are not normally detrimental to the life of a switch if the surge is
within the maximum allowable pressure rating of the switch. Diaphragm actuated switches should not be subjected to more than 10 surges per day. More frequent surges will greatly reduce the life of the diaphragm.

Square D's FSG/FYG/FTG max out at rated pressure below 100psi
Square D's FRG/FHG & 9013G Series max out at rated pressure above 100psi

The FSG is the shrink wrapped product one finds in hardware, home improvement, and farm supply stores in USA rural areas for properties with residential wells with holding tanks.

Switches with higher pressure ratings are more likely to be available from specialty distributors, not the hardware store.

Square D's FRG also offers these features:

Pump shut down application:
The 9013FRG reverse action pressure switches
can be wired in series with the FSG standard
action normally closed (N.C.) pressure switches
to automatically shut off pumps in case of
emergency such as power loss or when a
pipe bursts.

Low level alarm application:
The 9013FRG reverse action pressure switch
can be set to trigger an alarm based on the
low pressure conditions.

Manual on/off switch:
The 9013 series offers an optional on/off lever
for the pressure switch. This allows you to
manually turn on and off your pump system for
extended periods of time such as when you are
going to be away or have remote locations not
regularly in use.

Automatic low pressure/water cut-off
If system pressure is lost for any reason, a low
water condition for example, the automatic
low pressure/water cut-off feature will open
the contacts, turning off the pump. The low
water cut off functions normally and cycles the
pump per your typical demands, however, if
the system pressure is lost for any reason, the
switch contacts open, turning off the pump.

(from a data sheet, pg 4, at

http://ecatalog.squared.com/pubs/Machine Control/Condition Sensors/9013HO0801.pdf

 

[mikthebik]

Just want to thank everyone for your help. I think the suggestion of the pressure switch would work based on your responses. I'll do a bit more looking and plan to get a test model and simulate some breaks to see how it works. I'll also plan to install a pressure regultor to bring the static pressure down to the 70-80 psi range. That should help the pipes and make the selection of a pressure switch easier. Once I've got something I plan on sharing it with the water district, I know they'd like to find an inexpensive solution for their other customers.

Thanks again,
Mike C.