Plumbing 101a | Flow vs Pressure

Steve — Tue, 22 Dec 2009 21:05:45 +0000

As a service plumber, one of the most common plumbing problems that I have been asked to diagnose is low “water pressure”. The reason that I put “water pressure” in quotes is because what a customer thinks is low water pressure is quite often actually low flow. There is a difference, and that difference is very important when trying to figure out the best remedy for the problem.

Typical pressure regulator

So what’s the difference? Pressure is the amount of force behind the water, pushing it through your pipes. It is measured in pounds per square inch (psi). Flow is the amount of water that “flows” out of an open outlet, like an open hose bib or faucet. Flow is usually

measured (in the US) in gallons per minute (gpm). The symptoms for low pressure and low flow can sometimes look similar, but it is usually pretty easy to diagnose.

Pressure

The hot and cold water in your plumbing system is under constant pressure. The ideal pressure for an average home is between 55-75 psi. If your water is supplied by a public utility company, the pressure to your home is determined by a number of factors – none of which you have control over. If you have a private water source, you have a bit more control. The first thing to do if you feel you may have pressure issues is to go to test it.

Most home improvement or plumbing supply stores have pressure gauges that you can buy for about $10 or so. Get one that will screw onto a hose bib. Screw it onto the hose bib that is closest to your water main, turn the bib on, and see what the pressure reads. If it is between 55-75psi, you don’t have a pressure problem. You should also check to see if you have a pressure regulator (PRV). They look like the picture at the top of this article.

pressure gauge

If you do not have a PRV and the pressure is too high, call a plumber and have them install one.
If you have a PRV and the pressure is too high, the PRV is likely bad and needs replacement.
If you have a PRV and the pressure is too low, you can try to adjust the PRV. If that doesn’t work, check your neighbor’s pressure. If theirs is too low as well, it is likely not your PRV, but a problem with the municipal supply. If theirs is fine, your PRV is bad.
If you don’t have a PRV and the pressure is too low, you can try checking your neighbor’s pressure, but it will likely be the same. It’s a problem with the municipal supply, and there’s not much that can usually be done.

Flow

This is the category under which 75% of the problems I have seen have been. If you keep in mind the way in which plumbing is run, figuring out what the problem here is can be fairly simple. If the pressure to your home is fine, but you are not happy with the water supply to one or more fixtures, it pretty much has to be a flow problem. I drew a simple example of how the water supply plumbing is run on a typical house. Hot water is red, cold water is blue.

simple plumbing layout

By understanding the layout, it is much easier to figure out the cause of your flow problem. Let’s look at some examples:

Let’s say, for instance that you have very little flow to the hot water side of you bathtub. All other fixtures are fine. That would mean that there is an obstruction of some kind either in the small section of line from the main hot water line to the fixture, or in the hot side of the faucet itself. See below:

If, on the other hand, the hot water flow to the entire house is low, the obstruction would have to be either right at the water heater or in the short section of hot water piping between the water heater and the branch line for the washer. There is a small possibility that the cold water plumbing feeding the water heater may be the culprit, but it is much more likely that the hot line is at fault. See below:

One very common scenario is a single fixture with low flow (both hot and cold side). This is almost always due to a clogged aerator. Calcium from the water heater and/or rust from galvanized water lines or the water heater will build up in the faucet aerators and reduce the flow to that fixture. In this case, the solution is as easy as removing the aerator, cleaning it, and reinstalling. That will usually be enough to restore flow to that fixture.

To remove the aerator, I recommend using small “channel lock” type pliers. Wrap the jaws with electrical tape to keep the pliers from scratching the finish. Remember “righty-tighty, lefty-loosy”. Refer to the diagram below for further info.

One final point to keep in mind: An obstruction in your water supply lines will not lower your pressure; it will lower your flow. Understanding this can really help with diagnosing your plumbing issues. Do your best to try to narrow the problem down, and take care of simple things yourself. Call a plumber to fix those things that you cannot handle yourself. Either way, getting a jump start on the diagnostics can save you tons of time and money on your plumbing repairs.

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Why Plumbing Info?

Steve — Thu, 19 Nov 2009 05:23:04 +0000

Hello, Steve here. Welcome to Plumbing Info.org. If you don’t know who I am yet, you may want to read my “About Me” page before reading further.

So, I guess the question is: why does this website exist?

Well, you can relax, because, unlike 99.9% of the websites on the net, I am NOT trying to sell you something. You will find no affiliate links anywhere on this site. The ONLY way I can make a penny off this website is if:

You choose to click on one of the sponsored links
You choose to make a donation

Now that that’s over, let’s get down to plumbing!

Spending a lot of time at home over the last couple of months has given me a chance to reflect on my career and all that I have seen in my more than 15 years as a plumber. When I look back on it, I realize that the most important aspect of my career was my customers. Every job I did was dependent upon the interactions between me and my customers. The best and most satisfying work I ever did was when I was working for people that were knowledgeable and capable of making informed decisions.

Why is that? There are several reasons.

People that know what’s going on keep me on my toes. Someone who knows nothing about plumbing knows nothing about what I am doing. I can be lazy and “cut corners” and they would not know that difference.
People that know plumbing appreciate the value in what I do. It is nice to be appreciated by a customer that knows that the work I did was top notch. I can sense when someone knows that they got quality work.
People who know the game cannot be taken advantage of. When a person has had bad experiences with plumbers, it is all that much harder to get them to trust an honest plumber.
People who know their plumbing system are far easier to communicate with. I cannot count the number of times when I arrived at someone’s house and had them tell me “the trap is on the roof” or something equally unhelpful. It seems like it takes forever to get them to a point where they can actually give me information that I need (“the toilet is backing up into the bathtub”).

I actually have another reason for starting this website. The long and short of it is that it is not possible for me to interact with people in a service environment for so many years without actually caring about how they are treated. I have spent so many years, watching what some other “plumbers” did or seeing the work they left behind and shaking my head with disgust. In the past, I had the option of outperforming them and making them look silly. That is no longer an option, however. I hope that this site will actually do more than that. I hope that I can affect thousands of people, who will, in turn learn what they need to make sure that the bad plumbers and the cheats fail and the plumbers who worked hard to get where they are, by giving quality work at a fair price succeed.

So, why should you read this? There are so many benefits to you being “in the know” that I can hardly list them all, but I will list a few.

You will only hire qualified plumbers
You will only hire plumbers that do quality work (there is a difference)
You will get the work you need done done correctly
You will save money (lots of money)
You will be able to choose what work you need to do now vs. what can be done later
You will never be taken advantage of again
You will have information that a lot of plumbers do not want you to know

There are many more, of course, but I will leave them up to you to discover.

Talk to you soon!

Steve

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Plumbing 101a | Flow vs Pressure

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