Frozen pressure gauge

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Old 05-17-15, 04:16 PM
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Frozen pressure gauge

The pressure gauge on my irrigation system was damaged during an unexpected freeze one recent night. It was mounted directly on a tap on the pump. If I replace it and use an extension of 4"-8" to create a vertical air column, will this keep a new one from freezing or will water work it's way up to the gauge anyway? AND will it reflect the pressure the same whether it's measured against water or the compressed air column? (According to ol' Bernoulli, it should be the same!)
 
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Old 05-17-15, 04:36 PM
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Water can't be compressed. Air can. I don't think you'll get an accurate reading. and yes I think it will still freeze. I doubt you can keep moisture away from the mechanism with just an air column.
 
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Old 05-17-15, 06:05 PM
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Your idea of the vertical pipe nipple will probably help. It might not be 100% foolproof for years and years but it can't hurt. My first question is; why do you need the gauge? If the system works what do you care about the pressure? I like sausage without knowing what goes into it.

Having the gauge mounted above and with a vertical pipe nipple will create a air bubble that will keep the liquid water out of the gauge. Because air is compressible it will be at the same pressure as the water and transmit the water's pressure to the gauge.

The one thing I don't know is what the water vapor will do. Most gauges are bourbon tube style. They have a copper or brass tube formed into a coil. One end is sealed and the other is connected to your water system. As the pressure of your water increases it causes the coiled tube to straighten and gears and levers convert that movement to make the needle move. Water vapor may eventually get way up into that bourbon tube and condense into liquid water which could freeze but much of it would be sloping downhill and allow the water to drain out.
 
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Old 05-17-15, 06:13 PM
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Eventually that small section will get waterlogged and be ineffective, but I imagine you drain the system every year? That alone should recharge the air in the pipe.

Do a search for old school water hammer arrestors...basically you are creating a small riser just like plumbers used to do.
 
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Old 05-17-15, 08:22 PM
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Reason for pressure gauge

Thanks guys for the advice. The reason I like a pressure gauge is this system is agricultural and uses a high-head pump to run sprinkler lines up a hill with 90 feet of head. At the bottom of the hill I sometimes need to simply pump water into a planted trench to more or less flood irrigate it. I found that unless I curtail the flow appropriately, the amperage draw on this 7-1/2 hp pump rises to levels that cut out the 3-phase heater coils and stop the motor. I have monitored the current draw with a clamp-on ammeter to set the appropriate flow, but this is a nuisance and probably not the safest thing to do when I have to work in a 440-volt control panel. However, I found there is a good correlation with the amount of pressure I maintain and the current draw and can thus preclude taking current readings. A pump working against a head of pressure draws less current than one simple pushing (lifting) a larger volume of water without much pressure. Sounds counter-intuitive, but that's the way it works.
 
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