I have a banging pipe question?
Let me give you a little info:
The house is about 10 years old
It’s a two story house with the lower level below the road level on a hill.
We are on city's water, not a well.
I have two injector pumps one for the lower level and one for the upper level, the house is below the public sewer line.
I also have fire sprinklers which do not have a shut off valve and are at a very high pressure 90PSI.
The city's water tanks are a 1/2 mile away and about 100 feet below our home.
Every morning and my pipes bang and squeak, no water is running and the lawn sprinklers are off.
I can watch the pressure gauge on the fire sprinklers bounce about 40PSI.
The banging is getting worse and more frequent.
I have checked the pipes that I can get too, under the house and they are secured with hook type nails and clamps.
How do I stop the banging and squeaking?

My first though is that city water pressure is varying wildly as customers down the line use a large volumes of water. Do you have a pressure regulating valve on the main line from the street?

I'm beginning to wonder if the noise could be coming from the ejector pumps or their check valves. It sure would help us if you could tell us exactly what pipes are banging. Regards, Tom

Hksroud,
Those are my thoughts exactly!

The pressure gauge is on the line that feeds the fires sprinklers. It's inside the wall. It has an access panel and a clear out valve, I can provide pictures.

I don't know what to do about it if is a water pressure/flow issue?

Add a one way valve?

Speedball1;
As for the ejector pumps, they only work when their small tank fills. I don't see any water lines attached to the pump or the catch basin. I have had one of the pumps replaced (what a mess) and very expensive.

Don't know much about what the pressure of sprinklers should be. I would assume that there is no shut off valve for sprinkler so that they cannot be accidentally turn off. At 90 lbs you certainly should have another PRV for the rest of the house. Do you have a valve to turn off the water to the rest of the house?

Don't know much about what the pressure of sprinklers should be. I would assume that there is no shut off valve for sprinkler so that they cannot be accidentally turn off. At 90 lbs you certainly should have another PRV for the rest of the house. Do you have a valve to turn off the water to the rest of the house?

There's a water shut off valve on the main just before it goes into the house. Also a Bell shapped valve above that, that has a nut that can be used to adjust the water pressure.

The bell shape valve would be the PRV for the house. Is the line to the fire sprinklers connected before or after the PRV?

I think the PRV is after the Fire sprinklers

The first phot shows the Main Waterline.
http://i595.photobucket.com/albums/tt35/Timster1961/WaterPipes.jpg?t=1282495291

This picture shwos theback side where the Fire sprinkler valve and pressure gauge is
http://i595.photobucket.com/albums/tt35/Timster1961/FiresSprinklerSystem.jpg?t=1282495291

Next time you have the noise, feel along the fire sprinkler pipe, above the pressure gauge to confirm that the pipe is moving or vibrating. If it is, check code and fire sprinkler literature about the installation of a PRV valve and the minimum pressure required for the fire sprinkler system. Cut the pipe above the tee with the pressure gauge, install a PRV and set at or above the minimum pressure required for the fire sprinkler. Above the PRV, install another tee. Install another pressure gauge out the side of that tee.

Looks like you got it all. The red handled valve is a clean out for the Fire Sprinkler system. I was told by the build to clear out the pipes once a year. It drains out near the main just to the right of the PRV (90 degrees, points down) shown in the first picture.

I see it now.

As a fire sprinkler expert, the bsnging piping is probably due to entrained air in the sprinkler system. If the pressure gauge is moving back and forth on the system, usually that would inidcate trapped air in the system. See if an air vent valve could be installed at a remote location opposite to the water supply connection. When the system is filled, there is no place for the air to go, unlike your plumbing system, which can vent out the air through use of the fixtures. I would not advise the installation of a pressure reducing device on the sprinkler system without consulting a licensed fire sprinkler contractor or engineer. You could reduce the pressure in the sprinkler system to the point of system failure if not careful. The valve on the system riser is a test/drain valve, used to test the alarm device(red box), and to drain the system. If that does not work, you could install a pressure chamber on the main water line that can absorb the pressure surges without causing water hammer.
Greg Bartels, Local 669 Sprinklerfitters Instructor