Double Check Valve Assembly - Field Test
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- čas přidán 2. 01. 2014
- How to test a double check valve assembly with a three valve test kit. Testing differential pressure, for backpressure, No-Flow status, and the downstream shut off valve for tightness. Video can be viewed at www.ceuplan for CEU credit for Drinking Water and Waste Water Operators and well as certified backflow testers.
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Great video. Just took the backflow prevention device tester training course at nwwa with as the teacher. Did a awesome job teaching the material would recommend taking the course if you want to become a backflow tester.
Thanks for making this. I have severe learning disabilities and am practicing 5 months ahead of my level 3 and this really helped
InstaBlaster...
The video was awesome....In great detail...THANKS...
This was very clear and helpful!
Nice and easy demonstration!
yup nailed it.
VERY GOOD DESCRIPTION OF DOUBLE CHECK VALVES ...
Excellent Video. I have a situation pointing back at a backflow preventer that appears to be loosing around 80kPa (above the allowable limit) at flow. It is quite new and I'm suspect of it not being properly commissioned or it is blocked somehow.
Can I measure this loss at flow? or do you recommend why this backflow might not be operating correctly.
Neil backflow prevention devices will loose pressure in a flow condition. The AWWA specifications state that a double check valve assembly should not loose more than 10 PSI (68.9kPa) across the check valve. 80kPa is equal to 11.6 PSI therefore, the backflow prevention device assembly does not meet the AWWA specifications. The AWWA pressure loses represent the maximum permissible pressure loss at any flow rate up to and including the rated flow rate of the assembly. To measure the pressure loss across the assembly during a flow condition one can use a standard pressure gauge to measure the pressure at test cock #1 and test cock # 4 and calculate the difference or one can use a backflow test kit to measure the pressure loss by connect the high pressure hose to test cock #1 and the low pressure hose to test cock # 4. The pressure loss could be due to the springs tensile strength. Restricted flow could such as a blockage or the assembly is undersized --to small for the rate of flow. If the assembly is sized smaller than the inlet piping this could cause a restriction in flow and as the velocity increase the pressure decreases.
Thanks for the video. The fix where test cock #4 has higher pressure on the first test would be just to replace the shutoff valve right? I guess we could try opening and closing a few times also to see if it releases something that might’ve been lodged.
Yes. Rick, if backpressure is present at test cock number four, the downstream shut-off valve is not drip tight. Try reclosing. If the backpressure does not diminish, replace, or repair the downstream shut-off valve. Test the assembly if you can eliminate the backpressure.
Is this another way instead of using a sight tube?
Yes this is another way of measuring the differential pressure across the check valve other than using a sight tube. Measuring the differential pressure can be accomplished by using the differential pressure gauge high and low side pressure hoses. In the test kit, the high side measures the pressure on the inlet side of the check valve and the low side measures the pressure on the outlet side of the check valve. The differential pressure gauge calculates the actual difference in pressure across the check valve. When using the a site tube, the high side is measuring the pressure on the inlet side of the check valve and the low side is measuring against atmospheric pressure. In this methods, the check valve in a DCVA should hold 1 psi greater than atmospheric pressure. Both are industry acceptable methods of measuring differential pressure. The AWWA M14 Fourth Edition of "Backflow Prevention and Cross-Connection Control" illustrates both testing procedures or methods.
Jimmy Backflow what are you measuring with the sight tube? Differential also?
You are measuring atmospheric pressure in the vertical tube. Once the water stops flowing from the vertical tube the water pressure on the outlet side of the check valve is atmospheric. Atmospheric pressure is 14.7 psia. If the check valve is holding, the pressure on the inlet side of the check valve is greater than atmospheric pressure. The differential pressure across the check valve is the difference between water at atmospheric pressure and actual water pressure. The high side of the test kit is reading 15.7 psia and the low side of the test kit is reading 14.7 psia, giving you a differential pressure of 1 psid on the test kit. Absolute pressure and gauge pressure are related. Absolute pressure is equal the gauge pressure plus the atmospheric pressure. If there is no pressure on the gauge (low side) other than atmospheric, the gauge would read zero. Refer to the EPA Cross-Connection Control Manual Chapter 3 for more information regarding atmospheric and gauge pressure.
Jimmy Backflow my paper says DCV closed tight or leaked and if it closed tight wants the PSI. I can't use just the high and low right? I have to use the high and sight tube for that PSI right. Not just bleed high and low. That would be way easier since my backflow are in the ground
The industry standards state that a DCVA check valves shall have a static differential pressure across the check valves of at least 1.0 psid. You should be recording the differential pressure drop across the check valves on the test form. As the video shows you can use the high and low pressure hoses to measure differential pressure. The differential pressure drop across the check valves can be measured by connecting the high pressure hose to inlet side of the check valve and the low pressure hose to outlet side of the check valve. Record the PSID reading on the test kit on the report form. If the reading is 1.0 pisd the check valve is closed tight. If the reading is 0 psid, the check valve is not closed tight. A reading of greater than 0 psid but less than 1.0 psid indicates that the check valve is holding tight but does not meet the industry standards. Whether you use the vertical tube method or the two hose method, the differential pressure results will be same. Again, all you are trying to accomplish is to measure the pressure on the inlet and outlet side of the check valve and record the difference in pressure. The differential pressure across the check valves can be accomplished by installing the high side pressure hose to a test cock and the low side pressure hose to another test cock. This will give you an accurate differential pressure reading across the check valves as required by the industry standards, after the air is bleed from the test kit. Follow the video and report the differential pressure readings on the report form.
Thank you for a detail explanation of a backflow testing. Is it possible to make a simple testing tool for DIY purpose of check valve # 1 and #2 testing like using a evaluate for backpressure as you made ? I barely passed check valve #1 testing in last year and i failed check valve #2 with leaking. I think it was from o-ring on seat kit and I replaced it. I am sure it is ok now. But I don't know 100% if it is ok. Pluming company charge $150 for just testing. Would you please help me out to save the testing cost. Thanks
Thanks for watching the video. Simple test. To measure the differential pressure across the DCVA, check valves, close the downstream shut-off valve, and connect a standard pressure gauge (200 psi) to test cock #2. Open the test cock and record the pressure reading. Close test cock #2, remove the gauge, and connect it to test cock #3. Open test cock #3 and record the reading on the gauge. Subtract test cock #3 reading from test cock #2 reading. The pressure loss across the first check valve must be one psi or greater. For the second check valve differential, conduct the same steps using test cock #3 and #4. The pressure loss across the second check valve must also be one psi or greater. This procedure works, providing there is no downstream demand.
@@JimmyBackflow Thank you for your answer. Actually I have watts LF909 and i know the Backflow is tested on RPZ. Is it same way to test #1&2 check valve for RPZ ? I am not sure if you receive my email. Please see it and kindly reply when you are free. Thank you again.
@@jeonghwanbae2111 A simple test for the RPZ would be to follow the procedure previously stated to confirm the DCVA check valves. To test the opening point of the RPZ, connect a pressure gauge with a bleed attachment as seen in the DCVA video (best to use 0 to 100 Psi or less) to test cock #2. Open test cock #2. With the gauge reading pressure, close the upstream and downstream shut-off valves. Next, open test cock #3. When the water stops flowing out of the test cock, the gauge reads the static pressure upstream of the first check valve. Next, open the bleed valve on the pressure gauge. Water discharges out of the relief valve, and the gauge reads the opening point of the relief valve.
@@JimmyBackflow Thank you so much. I measured the pressures for each cock #2&3&4 and found the differences between them. I tried to measure 2&3 in one time per your class but I am in difficulty to find correct gauge with my tool. I am going to send 4 pictures showing the pressure of each cock for your advice, if you don’t mind. Thanks
Actually if back pressure is a possibility, the device should be replaced with an RPZ.
The DCVA is approved for backpressure situations. I refer you to ASSE, USCFCCCAHR and AWWA. What are the bases for your statement?