Flow rate problems

[David Daiker]

I did some searching but could not find much about low flow rate problems. If my search foo failed me I apologize.

I've been in my home for 16 years now, it was built in 1997. My "water pressure" was never great but livable. By "water pressure" I really mean how much water can I push through my system at once. If we are using the shower what happens when we flush the toilet, etc. In recent years we've noticed that this has gotten really bad. If we are taking a shower and we use any water anywhere else (except the toilet in the same bathroom for some reason) the shower goes down to a trickle. We've also noticed a significant reduction in the how much ground we can cover when watering the lawn. I've installed low flow shower heads, turned my toilets supply line to 1/2 open and adjusted my pressure regulator so I have about 75psi but still no joy.

I measured my flow using the bucket and stop watch method and came up with about 2.5gpm. This is from a hose spigot very close to my line coming in the house. It comes in the house in a 3/4 copper pipe, then to my water softener, then to a 3/4 3/4 1/2 T. The 1/2 goes to the host spigot and the 3/4 goes to the rest of the house. Probably less than 20' of pipe from wall to spigot.

I measured the flow with the water going through the softener and with the softener's bypass on. About the same results (well withing margin of error of a bucket measurement).

Is this kind of flow rate "normal"? Is there anything I can do about it as a DYI project? Is there something a plumber can do about it?

 

[Jadnashua]

IMHO, a 3/4" pipe, with cold water, should easily exceed 10gpm with the supply pressure you have. Now, it could be your PRV is failing, or something in the softener. Are there any galvanized pipes or fittings in your system? If so, they're probably the source of the problem as they do rust internally, often to almost enough to block the flow before they rust through. Also, many PRV's have inlet filters, and over time, that could be clogged up. If it's a supply problem from the street, you may need to dig things up and find the problem. In most places, you own that line, but it might be the utility's, then they would have to fix it.

 

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[David Daiker]

Thanks for the advice. We actually had the supply to the house replaced a couple of years ago due to a "blue max" pipe failure. I had them put in a new main cut off valve but did not replace the PRV. So even if my pressure is 75psi it could be the PRV that is causing my flow problems? The main supply to the house is 3/4 but by the time it gets to any fixtures it's stepped down to 1/2 (including the hose spigot I tested on). What would you expect from a 1/2" pipe?

Can I test the flow rate at the street some how? Maybe they botched the job when they replaced that line.

 

[hj]

A bad PRV CAN maintain pressure when there is no flow but not allow full flow when any water is used. What kind of pipe and what size did they use to replace the main line?

 

[Reach4]

So even if my pressure is 75psi it could be the PRV that is causing my flow problems?

Some PRVs have screens. Maybe yours needs cleaned.

It would be nice if you had a tap before the PRV to know what the pressure was before the PRV.

You could measure the pressure at a hose bib while somebody is filling the tub. That would give another data point.

 

[David Daiker]

A bad PRV CAN maintain pressure when there is no flow but not allow full flow when any water is used. What kind of pipe and what size did they use to replace the main line?

It looks like standard 3/4" copper coming out of the wall.

 

[David Daiker]

Some PRVs have screens. Maybe yours needs cleaned.

It would be nice if you had a tap before the PRV to know what the pressure was before the PRV.

You could measure the pressure at a hose bib while somebody is filling the tub. That would give another data point.

No go on the tap, in fact I don't have any taps anywhere, other than the fixtures of course. I measure the pressure with the tub filling tomorrow.

How can I tell if my PRV has a screen? Is that something that is usually cleanable without taking the whole thing apart?

 

[Reach4]

No go on the tap, in fact I don't have any taps anywhere, other than the fixtures of course.

You said "The 1/2 goes to the host spigot " which I presume meant hose spigot. That water does not go through the softener, right?

How can I tell if my PRV has a screen?

What is the make and model? Look for a label. If no label, look for a brand emblem and post a photo including the emblem.

 

[Jadnashua]

Does your softener have a bypass? Does the flow improve if you bypass it? Other than that, you'd need to probably either service or replace the PRV.

The copper institute calls for a maximum velocity of water in copper pipe to be less than 8fps with cold and 5fps on hot. Translating that to the size of the pipe means about 4gpm with 1/2" copper for hot and 8gpm on hot for 3/4". Bump those numbers up 60% for cold. Yes, you can draw more than that, but it's not recommended, at least on a continuous basis (something you'd not expect in a home). Higher velocity can cause noise, and literal wear on the insides of the pipe. You get more friction when running it faster, which can affect the working pressure, too. Static pressure should be the same, regardless of the pipe size, but working pressure will depend on the flow rate and friction created by the flow and fittings, especially those that change direction.

 

[David Daiker]

You said "The 1/2 goes to the host spigot " which I presume meant hose spigot. That water does not go through the softener, right?

What is the make and model? Look for a label. If no label, look for a brand emblem and post a photo including the emblem.

The hose DOES go through the softener, the T is after that. If I have the valve replaced I'm going to have them change that and split the hose off before the softener.

The PRV is a WATTS N358. Here is the pic.

 

[Reach4]

http://media.wattswater.com/1915088.pdf shows "(77) Strainer" in the diagram.

The N35B, and the N35B-RK repair kit have been discontinued. I don't know if there is a direct replacement.

I would consider getting a new PRV, and I would consider getting a connection for a pressure gauge at the input to a new PRV if I had one installed. It is even possible that you no longer need a PRV. I am not saying that is likely.

It is usual to not have the outside faucet go through the water softener, because unsoftened water is better for plants. Soft water would be nice for mixing lawn chemicals in your sprayer.

 

[NickK]

It sounds like you might greatly benefit from a thermostatic shower cartridge rather than a pressure balanced cartridge. Pressure balanced cartridges regulate water temperature by detecting changes in water pressure. So lets say you flush the toilet. This raises demand on your plumbing system for cold water necessary to refill the tank. If you are using the shower at the same time, the pressure balanced cartridge detects that cold water is flowing elsewhere. To compensate it drops the pressure of the hot water in proportion. This keep the water at a safe, warm temperature - but the flow rate is also reduced. In newer homes this is often not a problem but in older homes or homes with lower water pressure coming in from the city you could experience annoyingly low pressure. Any answer could be a thermostatic shower cartridge. Thermostatic cartridges do not regulate temperature using a pressure balancing method. Rather they truly sense the temperature of the water (more similar to a thermostat). The water flow is regulated based on the temperature, rather than pressure. It's a little hard to explain but if you take the case of Delta 17 series and 17T series cartridges one is pressure balanced and the other is thermostatic. You can read much more detail here: the differences between a Pressure balanced 17 series and thermostatic 17T series Delta shower cartridge. You solution may be to change to a shower with thermostatic cartridge. It doesn't have to be Delta brand - most major brands have a thermostatic option.

 

[hj]

Just remember, a thermostatic valve operates by REDUCING the hot or cold to maintain the temperature. IF the cold pressure is reduced it will HAVE to reduce the hot flow to keep the temperature constant, which could make it act like a pressure balanced valve.