When testing a backflow prevention assembly with OSY or NRS valves on a dry fire sprinkler system the simple act of closing shut off valve #2 can build up enough pressure on the upstream side of the Clapper valve to trip the system. It happens to many backflow testers every single year, it has never happened to me because I follow these simple steps.

1. In the photo there are 2 gauges, the lower gauge is the water pressure on the upstream side of the Clapper valve. The upper gauge is the air pressure on the downstream side of the Clapper valve. The air pressure is what keeps the Clapper valve closed. There are many different dry systems on the market and some systems require more air pressure than others. If the readings are equal to the values below you are in little to no danger of tripping the clapper valve when testing the backflow prevention assembly.
2. Water PSI = Air PSI

   60-80 PSI = 30-35 PSI

   80-100 PSI = 35-40 PSI

   100-120 PSI = 40-45 PSI

   120-140 PSI = 45-50 PSI

   If your air pressure is lower than what is indicated on the above chart for a given water pressure that “may” indicate a problem and you should inform your customer and make it clear you are not certified in dry systems and it would be wise to have a certified technician inspect it.

3. As you’re slowly closing shut off valve #2 on the backflow preventer keep an eye on the lower water pressure gauge on the dry system. If the needle begins to rise STOP what you’re doing and slightly open test cock #4. The water pressure gauge on your dry system should drop back down to the original reading. Continue to slowly close shut off valve #2 while continuing to watch the gauge; the water pressure should remain stable. Once you have the shut off valve closed tight you can close test cock #4 and begin your test.
4. If the air pressure is much lower than the chart above for a given water pressure your best option is not to touch the assembly until the dry system has been checked out by a certified technician.
5. Remember it is extremely important to know what the downstream process is before you shut the water off. It’s up to you to educate yourself on the various types of systems to avoid costly damages to the equipment downstream of the assembly.

                     “Here is an improper installation with multiple deficiencies.”

1) System has an unprotected bypass, this is not allowed.

2) Backflow assembly is not mounted per manufactures written specifications; mounting bracket blocks the ability to repair this assembly.

3) The Wye strainer is installed downstream of the backflow preventer. In order for the Wye strainer to perform its job and prevent debris from impeding check valve operation it must be installed upstream of the backflow preventer per manufacturer’s written  instructions.

4) Both check valves leaked on this DCVA because the internal assembly was filled with gravel, the contractor did not follow manufacturers written installation instructions and flush the lines before installing the backflow preventer.

It’s important to note: if the Wye strainer was properly installed upstream of the backflow preventer per manufacturer’s suggestion, it would have blocked the gravel from entering the assembly and jamming the check valves  in the fully open  position consequently leaving the city water supply unprotected.

Below is off of Watts basic installation instructions found on the 774 series:

Check with local authorities for installation requirements. Install valve in the line with arrow on valve body pointing in the direction of flow. Pipe lines should be thoroughly flushed to remove foreign material before installing the unit. A strainer should be installed ahead of the backflow preventer to prevent discs from unnecessary fouling.

CAUTION: Do not install a strainer when a backflow preventer is used on seldom-used water lines which are called upon during emergencies, such as fire sprinkler lines, etc.

This is an example of why it’s very important to “IDENTIFY” and “INSPECT” every assembly.

I sent an unmarked copy of this photo to several colleagues of mine and I asked them what they saw. They all assumed the last backflow tester failed to restore service to this existing assembly on a residential fire sprinkler system.

The problem is they are only looking at the backflow shut off valves #1 & #2. They failed to see that the fire sprinklers “Inspectors test/drain valve is in the open position,” and the “sprinkler system pressure gauge shows 0 psi.”

I do not know why the backflow assembly shut off valves are in the closed position and the inspector test valve is in the open position on this occupied residential property. What I do know is, if I restore service to this fire sprinkler system I will cause the alarm to sound and may cause property damage.

All I can do is return the system to the way I found it after I completed the test, then notify the owner of the situation, as well as inform the water department using the comments section on my test report.

Remember your USC training: NOTIFY, IDENTIFY, INSPECT, and OBSERVE.

Pics 1 through 3:

Here’s one for the good bad and the ugly. This is a 350ADA which the installer had converted to a Frankenstein RPBA/DCDA? I don’t know what you’d call this thing.

It was installed in 2013 and the CCS at the water district inspected the assembly at that time, but because the vault is small the relief valve went unnoticed.

The 1^st tester tested it is a double check and got acceptable values in 2013. In 2014 I tested it as a double check and got good values. This year I go to test the assembly and suddenly my feet get soaked. I bend down and discovered the relief valve. The relief valve must have been stuck closed for the 1^st two testing sessions.

I immediately put the system back online and went to see the CCS at the water Department. I explained what had happened and he was pretty surprised as he also initially inspected the assembly. I asked him if I can legally return the assembly to factory specifications? Because it still had the factory DC check modules installed it would only require a bulkhead assembly, cover plate, etc. Of course the CCS told me that it did have to go back to factory specifications.

Bottom pic:

I wanted to know why the relief valve did not vent for two different testers with 2 different companies for the 1^st two years.

Turns out someone had stuffed paper in the relief valve stem to keep it forced closed. Over time the paper must have compress and degraded, this explains why the relief valve did not dump normally when it finally did open. Obviously it could not open fully.

Click on photos to enlarge

I have just restored service for this improperly installed irrigation backflow assembly. This is a 1″ Wilkins 975XL RPBA which is installed below ground with no daylight drain. When this backflow assembly fails the box may fill with water and create a potential indirect crossconnection.

As a backflow assembly tester it is important  to note this on your test report  to relieve yourself of any liability.        Click photo to enlarge

The photo on the right is a good example of some of the improper new installations we run across from time to time.

Backflow preventer’s are required  t0 have 12″  of clearance below the assembly.  These look like they were installed  then covered up with dirt to set the boxes.

This is a Cam Check out of a 4″ Ames 2000SS, the area circled in yellow is typical of what you will find when these assemblies fail.

These rubber parts are not replaceable and this cam check had to be replaced.

click on photo to enlarge