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Measuring water pressure


Chris Bernhardt
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Is there a proper way to measure water pressure?

I find that the static pressure will sometimes be way high near a 100 pounds but the operating pressure when a fixture is opened in the house drops down to the 40 - 50 range.

What I have been doing is installing the pressure gauge on the exterior faucet nearest the main water supply pipe, reading the static pressure there with no flow in the house and then going to the kitchen faucet and opening that and then measuring the pressure again.

Chris, Oregon

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I'd like to hear the proper way to measure water pressure too.

I will say that 100psi does seem quite high. Also, when you turn on another faucet it shouldnt loose 1/2 the pressure at the testing location. It doesnt sound right. Sure the volume capability is effected when other faucets are turned on but the pressure available at the test location should'nt drop that much. A little maybe.

I tested my pressure at the laundry basin at 55psi. I turned on the bathroom faucet full blast and the pressure at the basin only dropped 5psi.

Maybe one of our gauges is on the fritz? Is it mine or yours?

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Both measurments are good to know.

A 3/4" and a 1-1/2" main would give you the same pressure reading when the test valve is closed. Once opened, the pressure would drop more in the smaller supply. The same thing would happen if the main valve was partially closed.

I would make note of the different drops and see if there is a pattern.

I would also test the pressure/flow as far away from the source as possible.

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Originally posted by Jim Morrison

Do you guys test the water pressure during every inspection?

Yes. I test & note it at every inspection. Normal pressure is supposed to be between 40-80 psi. Around here, I don't say anything about high pressure till it gets above 100 psi.

If the house has decent pressure, yet I see flaccid showers, then I know that there are constrictions in the supply or distribution pipes.

That's what was happening in the example that Chris gave at the top of this thread.

It's useful to know the pressure.

- Jim Katen, Oregon

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Originally posted by Jim Morrison

Do you guys test the water pressure during every inspection?

Yeah, on SFRs and townhomes. Only takes a few seconds, so why not? One added benefit is that I often find hose bibs with major leaks at the handle stems during the test. Just a washer or two to fix, but it would be a pain to a client the first time he/she tried to use it.

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We always comment on pressure, but it really the volume that we pay attention to. High pressure and low volume is more problematic. Every bathroom gets the same routine regarding water pressure/volume: walk in turn on the cold at lav, turn on cold at shower/tub, nudge stool with calf, flush stool - listen and look at water flow(s). We do no room vs room observations and our client is nearly always present.

WARNING! INSPECTOR LORE: Someone told me that a young man can pee at 35# and an average sump discharges at 15#: lot of difference in performance.

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I always check the pressure, along with generally noting how fixtures perform in the house. Clients are never happy with low pressure or weak flow. And like Jim, I don't automatically call for action just because the reading is above 80 psi. In certain areas around here 90 - 100 is normal (nearby and downhill from the local water association I've seen it up to 115; that I flagged). If the system isn't leaking anywhere the pressure isn't a big deal.

Brian G.

Love the Pressure (90 at my house) [^]

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Hi,

I don't bother to check pressure anymore. There are too many variables that can alter the results and trying to explain these each time just eats up too much time. I'm more interested in ensuring that there's plenty of water volume to support someone taking a shower at the same time that the washing machine and dishwasher are running and someone decides to brush their teeth, than I am in seeing what the pressure is.

There are areas of Seattle where water pressure is so low that if the builder uses the smallest diameter allowed by code the house will have deplorable water volume. On the other hand, in those same neighborhoods, if the builder uses a larger supply line from the meter into the house the volume in the home will be wonderful in spite of the low pressure in the street. Conversely, you can have a neighborhood with high water pressure; but if the house you're inspecting has occluded lines, the fixtures will perform like there's only 20 lbs of pressure.

What I do now is look to see how the hydrants are marked. If they're all green, I know that pressure in the street is 60 psi or better. So, if volume sucks at the house it's going to be the fault of an old occluded supply from the meter to the house or occluded/restricted lines in the home.

If a hydrant has a yellow cap or nose on it, I know that it will have between 40 and 60 psi and will still provide adequate volume in homes with a new 3/4 inch line or 1-inch older line that's not occluded, as long as the interior lines have been replaced, but it will suck with an old 3/4 inch line or occluded 1-inch supply line - even when the interior supply lines have been replaced.

If it has a red nose or hat, I know that pressure will be below 40 psi, in which case any supply line from the meter to the house that's less than 1-inch, or an older occluded 1-inch line, will probably not provide satisfactory volume, even if the home has been completely re-plumbed; but a 1-1/4 inch main line coming into a new building will provide plenty of volume regardless of the fact that there's less than 40psi in the street.

ONE TEAM - ONE FIGHT!!!

Mike

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Used to test, but don't bother anymore. The pressure is whatever the municipal supply is providing @ any particular moment, and it constantly fluctuates. Testing pressure is a quick snapshot of what's going on @ a particular time. That's all.

Flow, OTOH, is what folks really care about. I'll turn on all fixture @ the same time, then selectively turn them on and off depending on which riser sets are involved. I follow the general procedure that Les described.

Pipe size is critical; what Mike described about size variables is more important than pressure; doesn't matter how much pressure there is, if you haven't got the pipe to carry it, it doesn't matter.

If there's something that doesn't add up, I might test pressure, but haven't in so long I doubt I could find my gauge.

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The hydrant coloring system is particular to your area. There is a nationally recognized system, but it's not all that common. If it's used, hydrants will be painted not to what static pressure they offer, but to what flow they can deliver. It sounds like Mike's area uses the recommended system:

Blue - best - 1500+ gal/min

Green - good - 1000-1499 gal/min

Orange - ok - 500-999 gal/min

Red - rotten - less than 500 gal/min

Some areas that paint their hydrants all the same are starting to use colored reflective tape, painted caps(like Mike said), etc.

More common, though, is some nitwit village president that decides should be a certain color, because it's his favorite. Or someone thinks hydrants are ugly and shouldn't be seen, so they paint them dark green.

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Back to the topic:

I do test water pressure. I guess I'm not really sure why! It's just part of my little system, I guess.

More important, I operate multiple fixtures together to look for an annoying loss of flow. There's a lot of old galvanized pipe in my area - so it's good to show people the flow restriction.

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Originally posted by kurt

Used to test, but don't bother anymore. The pressure is whatever the municipal supply is providing @ any particular moment, and it constantly fluctuates. Testing pressure is a quick snapshot of what's going on @ a particular time. That's all.

That's interesting. Around here, our water is supplied from reservoirs that are at fixed heights. Pressure from the street doesn't fluctuate at all unless there's a very large draw somewhere (a fire hydrant is open or something equally dramatic). I've measured pressure at houses that I'd inspected years before and the pressure is always consistent within a pound or two.

As far as I can see, pressure to an individual house is consistent 24/7/365. (Superbowl commercials notwithstanding.)

- Jim Katen, Oregon

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Both the IRC and UPC require the installation of pressure regulators whenever the water pressure exceeds 80 psi.

IRC 2903.3.1 UPC 608.2

If you are measuring higher than 80 lbs,appliances like dishwashers and washing machines may be damaged, if you measure more than 80 psi, I would recommend that a Regulator be installed by a licensed plumber. Once you mention 100psi, you need to cyoa

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Originally posted by Jim Katen

As far as I can see, pressure to an individual house is consistent 24/7/365. (Superbowl commercials notwithstanding.)

- Jim Katen, Oregon

One would think, yes. When I used to test, I'd find varying rates all over the city. That's largely why I stopped testing.

Chicago metro has remarkably complicated & convoluted water supply issues; lots of pumping stations, water being traded through various vendors, etc. Lots of pumping stations.

Our most current code requires a pressure pump @ any house w/ <1 1/2" service to the street (or something like that; anyone remember what the right dimension is?). This is intended to provide balanced pressure to individual houses, but is, in part, also a sop to the the plumbers union; they like the extra work & equipment.

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I tested them all in the early days, but stopped about 10-15 years ago. When I weighed the effort and time it took to take a reading against the amount of useful information it yielded, it just didn't make any sense.

Burst washing machine hoses can happen at virtually any pressure. I don't think HI's bear any responsibility for them, unless you break them yourself.

Still, no harm in testing pressure, I was just wondering who went to the trouble,

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Originally posted by Jim Katen

Originally posted by kurt

Used to test, but don't bother anymore. The pressure is whatever the municipal supply is providing @ any particular moment, and it constantly fluctuates. Testing pressure is a quick snapshot of what's going on @ a particular time. That's all.

That's interesting. Around here, our water is supplied from reservoirs that are at fixed heights. Pressure from the street doesn't fluctuate at all unless there's a very large draw somewhere (a fire hydrant is open or something equally dramatic). I've measured pressure at houses that I'd inspected years before and the pressure is always consistent within a pound or two.

As far as I can see, pressure to an individual house is consistent 24/7/365. (Superbowl commercials notwithstanding.)

- Jim Katen, Oregon

Perhaps the municipalities install pressure regulators at the meters and that could be why the pressures are so consistant. They maintain a higher pressure in the main and reduce it at the meters for each residence.

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Jim, not negating your position, just defending mine.

I don't see how it is any different from any other thing we test. I haven't read the IRC in awhile, but I think it says that over 80 PSI should have a regulator installed. If it is over 80 PSI, recommend a regulator, how is that hard or time consuming? Most pex pipe is rated for 100 PSI. I think you would have a hard time defending the position that 125 PSI was OK if a pipe burst and flooded the house. Washing machine hoses can burst at any pressure but it is way more likely when the pressure is in the 100 PSI range. In hindsight, that quick test would have yielded some pretty useful information. I have had my meter peg out at 160, is that acceptable?

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Hey Fritz,

Clearly 160 psi is way too high, but I should think that there have been other symptoms of a problem like that, -water hammer when operating the fixtures being chief among them.

I don't have a problem with anyone who wants to go "above and beyond" so long as they know how to and why. My experience just told me that my time was better spent looking at other things.

Could be it's just a regional thing, but I just concluded t'weren't worth it.

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Originally posted by AHI

Originally posted by Jim Katen

Originally posted by kurt

Used to test, but don't bother anymore. The pressure is whatever the municipal supply is providing @ any particular moment, and it constantly fluctuates. Testing pressure is a quick snapshot of what's going on @ a particular time. That's all.

That's interesting. Around here, our water is supplied from reservoirs that are at fixed heights. Pressure from the street doesn't fluctuate at all unless there's a very large draw somewhere (a fire hydrant is open or something equally dramatic). I've measured pressure at houses that I'd inspected years before and the pressure is always consistent within a pound or two.

As far as I can see, pressure to an individual house is consistent 24/7/365. (Superbowl commercials notwithstanding.)

- Jim Katen, Oregon

Perhaps the municipalities install pressure regulators at the meters and that could be why the pressures are so consistant. They maintain a higher pressure in the main and reduce it at the meters for each residence.

That's true of some cities. But my point is that, in my area, municipal water is almost exclusively fed by gravity. They might pump into the reservoirs to maintain the reservoir level, but the water flows from the reservoirs to the homes via gravity. This makes for remarkably stable pressures.

In other areas, in Kurt's Chicago for instance, they rely on pumps. Those areas have pressures that fluctuate.

- Jim Katen, Oregon

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