Behind me is a system that is not operating at its optimum pressure.
I know for a fact that it used to work just fine, so something has happened recently to
create this problem.
Another thing to point out is it's not isolated at just one valve.
It is a system wide problem.
To do our troubleshooting we need to go to the water source.
We also need to have the right instrument to do the job correctly, and when diagnosing
pressuring problems you have to have a pressure gauge.
The first thing we need to know is how much pressure a properly designed system needs
to start off with at the source and how much pressure it's going to lose from beginning
to end.
A typical, well designed system will lose fifteen pounds from beginning to end, but
there is an exception and those are systems with reduce pressure assembly backflow devices.
Those systems lose twenty-five pounds.
In the system we have here, we have a reduce pressure assembly, so this system will lose
twenty-five pounds.
Behind me is a head that requires forty.
If I have a head that requires forty and I lose twenty-five pounds, I have to start off
at the source with sixty-five pounds of static pressure.
The fifteen and twenty-five pounds of pressure loss is a rule of thumb to help you with your
troubleshooting.
There are a lot of factors that can affect these values, but the fifteen pounds of loss
can be broken down even further to five, four, three, two, one.
You'll lose about five pounds of pressure loss through a water meter.
Four through the backflow device.
Three pounds of loss through a valve.
Two pounds through a main line.
One pound through the lateral line.
The breakdown for systems that lose twenty-five PSI is five, fourteen, three, two, one, because
the reduce pressure assembly backflow device loses around fourteen pounds of pressure instead
of four.
To conduct our test we need to go to the backflow device.
Okay.
Here we are at the reduce pressure assembly backflow device, and this where we're going
to do our test.
I'm going to go to the very first test cock as the water's flowing this way.
This is the first test cock that it comes in to.
This is actually going to test the pressure before the backflow device.
About five feet away from here is the water meter on the supply side.
What I'm going to do is put the gauge right here, and I'm going to test my static pressure.
Now, if you'll remember the head that I have out there needs forty pounds.
A system that has this type of backflow device will lose twenty-five pounds, so for this
system to work to begin with I need at least sixty-five pounds of static pressure.
I'm going to open this test cock and see what the static pressure.
Static pressure is when water is not in motion.
Okay.
I have ninety pounds of static pressure.
That is more than enough for this system to work.
I verified that I have enough pressure to begin with, so now what I need to do is turn
this system on to see what the dynamic pressure goes down to.
I told you earlier that the breakdown is five, fourteen, three, two, one.
I expect to only lose five pounds, because between here and the city mainline all I really
have is a water meter.
Okay, so I was expecting my gauge to go down by five pounds, because we talked about the
breakdown being five, fourteen, three, two, one.
I didn't lose five pounds.
My gauge went down to forty PSI, which means I lost fifty pounds of pressure when it went
from static to dynamic.
I know for a fact that there is a restriction from here to the city mainline.
At forty pounds here, it's not going to leave me enough pressure at the head, because I
still have another fourteen, three, two, one pounds of pressure to lose; which will leave
me with something like twenty pounds of pressure at the head.
I did find out that there's a gate valve between here and the meter.
I'm going to make sure it's opened up all that way, because that could be our problem.
Okay.
It turns out that the problem was in the gate valve after all, and that ends up being a
pretty easy fix for us.
It doesn't always work out like that.
Sometimes we have to dig up the entire line from the backflow device to the meter to see
what could have been causing the problem.
In some cases you might dig up an old piece of galvanized pipe that's corroded, or an
old pressure regulator that doesn't work, or you might find out that it is not a problem
at all on your side.
If that's the case, the problem is on the city side, and you'll need to call them to
get them involved.
Another situation might happen when you do your test, and you just lose the expected
five pounds of loss.
That means that your restriction now is on the downstream side.
I'm going to take my gauge, move it to the last test cock, test loss across the device.
If that checks out, then I know that my restriction is on the downstream side of the backflow
device.
For more in depth training on this subject and more, you can attend one of our live education
class.
Stop by your local Ewing branch to find out how or visit us online at www.ewingirrigation.com.