Out of all the videos i've searched for to explain what the heck is a backflow safety valve. this one is the ONLY one that nails it with it's instructions and how it works. ThaNk you so much for satafying my 1am curiosity.
Jonnny, no water flows from high to low pressure --- from left to right in this diagram. If backpressure is present downstream on the right side of the slide, this is now the high-pressure side. In this case, if operating correctly, the second check valve prevents the high pressure from flowing back into the inlet pressure. If a backshphonage situation is occurring in the inlet system, the pressure is subatmospheric and the pressure downstream of the backflow device assembly is atmospheric. The first check valve prevents non-potable from entering the system is operating correctly. The flow is from high to low.
do the check valves close with the supply open and #2 shut off closed? I have one spring with 1lb force--> I have 10 psi coming in--> 1 pound lost while overcoming the spring ---> I now have 9 lbs on the downstream side of the check. At what point do I get higher on the down stream side to over come the supply and close?
When the backflow preventer is in a static state no downstream demand the check valves are closed. When in a static state the pressure loss across the check valves is generated by the check valve springs. Typically, a minimum of one pound loss on each check valve. The check valves open when there is a flow through the device and a downstream demand. If there is a backpressure issue (higher pressure on the outlet side of the device) the second check valve should close drip tight if operating properly. I hope this answers your question and thanks for viewing the video. If you have any further questions, let me know.
I have an older irrigation system installed at my home. I have access to the outgoing pipe to the sprinkler in the basement. From there, it goes to a free-standing verticle PVC pipe with a sill cock on it, and on top of that is a schrader valve, that the irrigation companies uses to blow out the water before winter. There is no backflow preventer installed. My question is this. Since it appears to install a backflow preventer, I need access to the outgoing water line. I do have that access inside the basement but on the outside, if I were to install the backflow preventer there, I believe I would have to dig down to get access to the pipe after it leaves the sillcock and heads to the valve box. Is that correct? I don't believe I can install it on the vertical free-standing PVC pipe since not only does water come out there, but also the air pressure is attached there to clean out the irrigation lines. I have seen screw in backflow preventers but not sure that would work. Any suggestions would be appreciated. Thanks
You can install a pressure vacuum breaker on the PVC vertical line that leads to the sprinkler system, providing that the pressure vacuum breaker is 12 inches above the highest sprinkler head. Without seeing a diagram, I can't say for sure what is the best solution.
As stated by many plumbing codes, a dual check valve with intermediate atmospheric vent (ASSE1012) is required on the make-up waterline supplied to a residential boiler to prevent the hot boiler water from entering the potable water system.
+goldenglory79 The check valves are spring loaded and close when the backflow prevention device assembly is in a static state. If the check valves fail to close, the check valve will have to be repaired or replaced.. Typically it is the check valve disk that causes the check valve to fail. It does not seat properly and has to be repaced.
At 4:01 you say a pressure loss occurs across the check valve. Why is this though? I read that a check valve does not produce a change in pressure, and since no work is being done on the spring due to the lack of motion of the spring, it seems very unintuitive that a pressure differential would exist?
As the water moves through the double check valve device assembly, it must pass through two check valves that are spring loaded which cause resistance and reduces the pressure. The check valve springs are typically a minimum of one pound. The resistance of the check valve springs lowers the pressure on the downstream side of the check valves. The check valve will close when the flow through the double check valve device assembly stops. Once the check valves close , the water pressure downstream of the check valves is lower than the pressure upstream of the check valves. The closed check valve locks in the lower pressure downstream of the check valves thus creating a differential pressure across the check valves.
TC#1 is typically used for maintenance purposes and can be used to create a static state when the downstream shut-off valve is not drip tight. The purpose of TC#2 is to measure the pressure upstream of the first check valve. The purpose of TC#3 is to measure the pressure downstream of the first check valve and upstream of the second check valve. The purpose of TC#4 is to measure the pressure downstream of the second check valve. By knowing the pressure upstream and downstream of the check valve one can determine the pressure loss across the check valves. The differential pressure across the check valves of a DCVA shall be 1PSID or greater to comply with the industry standards. I suggest you view the testing videos for further information on testing.
Asking to understand, not to criticize. If the water pressure is reduced as it goes through the check valves, why isn’t the non- potable pressure reduced in a back pressure, backflow condition?
Backpressure is greater than the inlet pressure and is prevented from flowing into the potable water system by a closed second check valve. If the second and first check valves are not drip tight, the backpressure non-potable water will lose pressure due to friction factors as it flows in the unwanted direction. When water flows through the backflow prevention device assembly, the pressure loss is due to the spring-loaded check valves. If both check valves are not holding drip tight against backpressure, the check valves are open, and the check valve springs are not creating the pressure loss with the water flowing in the unwanted direction. With backpressure, some pressure loss may be present in the body of the assembly but insignificant.
Out of all the videos i've searched for to explain what the heck is a backflow safety valve. this one is the ONLY one that nails it with it's instructions and how it works. ThaNk you so much for satafying my 1am curiosity.
Thanks for the comment, and if you need any further information let me know.
This was an excellent presentation on how these devices operate and what happens when they are compromised. Thank you for putting this together!
Thanks for viewing and for the comment!
Thank you for providing and explaining this information. Clear, informative and helpful.
Thanks for viewing the video and you comment.
Perfect explanation. Thank-you!
Very clear explanation
5:22 , does this mean the water can flow from low psi to high psi from the direction of left to right?
Jonnny, no water flows from high to low pressure --- from left to right in this diagram. If backpressure is present downstream on the right side of the slide, this is now the high-pressure side. In this case, if operating correctly, the second check valve prevents the high pressure from flowing back into the inlet pressure. If a backshphonage situation is occurring in the inlet system, the pressure is subatmospheric and the pressure downstream of the backflow device assembly is atmospheric. The first check valve prevents non-potable from entering the system is operating correctly. The flow is from high to low.
thank you Jimmy for the video
do the check valves close with the supply open and #2 shut off closed? I have one spring with 1lb force--> I have 10 psi coming in--> 1 pound lost while overcoming the spring ---> I now have 9 lbs on the downstream side of the check.
At what point do I get higher on the down stream side to over come the supply and close?
When the backflow preventer is in a static state no downstream demand the check valves are closed. When in a static state the pressure loss across the check valves is generated by the check valve springs. Typically, a minimum of one pound loss on each check valve. The check valves open when there is a flow through the device and a downstream demand. If there is a backpressure issue (higher pressure on the outlet side of the device) the second check valve should close drip tight if operating properly. I hope this answers your question and thanks for viewing the video. If you have any further questions, let me know.
I have an older irrigation system installed at my home. I have access to the outgoing pipe to the sprinkler in the basement. From there, it goes to a free-standing verticle PVC pipe with a sill cock on it, and on top of that is a schrader valve, that the irrigation companies uses to blow out the water before winter. There is no backflow preventer installed. My question is this. Since it appears to install a backflow preventer, I need access to the outgoing water line. I do have that access inside the basement but on the outside, if I were to install the backflow preventer there, I believe I would have to dig down to get access to the pipe after it leaves the sillcock and heads to the valve box. Is that correct? I don't believe I can install it on the vertical free-standing PVC pipe since not only does water come out there, but also the air pressure is attached there to clean out the irrigation lines. I have seen screw in backflow preventers but not sure that would work. Any suggestions would be appreciated. Thanks
You can install a pressure vacuum breaker on the PVC vertical line that leads to the sprinkler system, providing that the pressure vacuum breaker is 12 inches above the highest sprinkler head. Without seeing a diagram, I can't say for sure what is the best solution.
I am searching about double check valve we can use it with Sulphoric acid 98.5 conc.
You need to consult with a manufacturer. They do make plastic backflow preventers.
Can I ask you a question? Why are central hot water systems often using double check valves?
As stated by many plumbing codes, a dual check valve with intermediate atmospheric vent (ASSE1012) is required on the make-up waterline supplied to a residential boiler to prevent the hot boiler water from entering the potable water system.
how do you reset the check valves when they trip
+goldenglory79 The check valves are spring loaded and close when the backflow prevention device assembly is in a static state. If the check valves fail to close, the check valve will have to be repaired or replaced.. Typically it is the check valve disk that causes the check valve to fail. It does not seat properly and has to be repaced.
Jimmy Backflow thank you
At 4:01 you say a pressure loss occurs across the check valve. Why is this though? I read that a check valve does not produce a change in pressure, and since no work is being done on the spring due to the lack of motion of the spring, it seems very unintuitive that a pressure differential would exist?
As the water moves through the double check valve device assembly, it must pass through two check valves that are spring loaded which cause resistance and reduces the pressure. The check valve springs are typically a minimum of one pound. The resistance of the check valve springs lowers the pressure on the downstream side of the check valves. The check valve will close when the flow through the double check valve device assembly stops. Once the check valves close , the water pressure downstream of the check valves is lower than the pressure upstream of the check valves. The closed check valve locks in the lower pressure downstream of the check valves thus creating a differential pressure across the check valves.
@@JimmyBackflow wow you replied to back to a video made 6 years ago. Respect
What is the purpose of the TC#1, TC#2, TC#3 and TC#4?
TC#1 is typically used for maintenance purposes and can be used to create a static state when the downstream shut-off valve is not drip tight. The purpose of TC#2 is to measure the pressure upstream of the first check valve. The purpose of TC#3 is to measure the pressure downstream of the first check valve and upstream of the second check valve. The purpose of TC#4 is to measure the pressure downstream of the second check valve. By knowing the pressure upstream and downstream of the check valve one can determine the pressure loss across the check valves. The differential pressure across the check valves of a DCVA shall be 1PSID or greater to comply with the industry standards. I suggest you view the testing videos for further information on testing.
very nice video
The training can be viewed at www.ceuplan.com for CEU credits.
Asking to understand, not to criticize. If the water pressure is reduced as it goes through the check valves, why isn’t the non- potable pressure reduced in a back pressure, backflow condition?
Backpressure is greater than the inlet pressure and is prevented from flowing into the potable water system by a closed second check valve. If the second and first check valves are not drip tight, the backpressure non-potable water will lose pressure due to friction factors as it flows in the unwanted direction. When water flows through the backflow prevention device assembly, the pressure loss is due to the spring-loaded check valves. If both check valves are not holding drip tight against backpressure, the check valves are open, and the check valve springs are not creating the pressure loss with the water flowing in the unwanted direction. With backpressure, some pressure loss may be present in the body of the assembly but insignificant.
@@JimmyBackflow I got ya. Love the content of your videos and appreciate you making them. Thank you for taking the time to reply my question.
gd video