Replacing HPA Accumulator with High Cracking Pressure Check Valve

I understand the benefits of an accumulator - less wear on pump, stored pressure when power dies etc. However, I'm wondering if the main benefit of instant pressure to misters can be replicated by using a 100 psi (or other desired pressure) cracking pressure inline check valve. Can't get my head around what would happen once the pump spools up to 100 psi and the valve opens (cracks):

a) The valve opening decreases line pressure to below 100 psi which results in the valve closing and not much reaches the nozzles before this is repeated, or
b) The pump overcomes this pressure drop, continues to build pressure keeping the valve open and the misters are only supplied with >100 psi pressure, the pump turns off and extra flow <100 psi is stopped by the valve.

What would be the effect of using a check valve in this manner at each nozzle vs a single check valve on the main line?

Lets assume a system with pump maximum ratings of 5.5 Litres per Minute/160 psi, 6x 1 mL per second nozzles and 10 feet of 1/4" tubing.

I think you mean Relief valves?

Check valves are to prevent reverse flow.

Thanks for your reply redi jedi. I do mean an inline check valve, some have a spring that lifts when there is is enough pressure on the inlet side to overcome the tension. This amount of pressure is known as the 'cracking pressure'. Once the pressure decreases below this value, the spring closes to prevent back flow. For John Guest check valves, the cracking pressure is about 1/3 psi.

Not sure if there is a certain type of pressure relief valve that is inline and will work in the same way - but the idea is not to vent excess pressure from the system to the atmosphere.

Using some sort of inline pressure control fitting that prevents flow if less than 100 psi and permits flow if greater than 100 psi, be it an inline pressure relief valve or high cracking pressure inline check valve, will the system work?

Solenoid valve, triggered by a pressure sensor or even a timer if you have a pressure gauge.

Dont confuse the cracking pressure of a check valve for a form of pressure control. There's no such thing as a "high cracking pressure inline check valve"

There are PRV's, which open at a set pressure and the exhaust can be plumbed to where ever you want.

I did think of a solenoid, triggered by a pressure switch but then realised that is halfway to a accumulator setup anyway. Don't get me wrong, I'm not being stubborn with the accumulator-less setup here - just would like to have an open discussion about the theory of this proposed design. I haven't done too much research into exact part selection but here is a 1/4" stainless steel inline check valve with adjustable cracking pressure between 50-150psig.

I guess you could get the same thing with a PRV if you plug the normal flow outlet and made the exhaust apart of the main line to allow this pressure to build.

I'd be grateful if we could move discussion away from specific part selection and more towards how such a system would function. If it does not work in theory, it saves going down the line of looking for a specific part.

Guess I need to change my statement to " I've never seen...." lol.

Ok...The first thing I can think of, without an accumulator there will be pulsing as the valve (whatever pressure control valve is used) opens and closes, creating water hammer. Also pumping against a closed valve to build pressure is very hard on a pump. They call it dead heading.

Long story short, you could build such a rig but I dont think it would last very long or function the way you want.

Thanks for your input. Thought it might be a bit of a pipe dream, but I have a few more questions. Understand what you are saying about deadheading - if there is no flow through the pump the water inside the pump heats up and causes damage. But is this really a problem if the line pressure is less than the maximum pressure rating of the pump (the flow rate at maximum pressure is zero)? Help me to understand how this is different to an accumulator setup - is the pump not building pressure in a closed system (just a larger one - but pressure is still less than the maximum pressure rating for the pump).

As for the water hammer situation the valve closes after the pump has been shut off and is already ramping down to 100 psi in this example. Even so, I think that there will still be a forward velocity when the valve closes so would result in water hammer (please confirm). I guess you would need another valve on the check valve inlet side that opens when the pump is off and vents to the reservoir. If there was a dump valve into the res for the misters connecting to the reservoir, could it just tee into that line? Getting complex now, ha ha.

In regards to dead heading, its not really about the heat. Its the fact that the pump is moving water but it has nowhere to go. Since water is not compressible the pump will either stall or start breaking vanes off the impeller. Note im talking about a centrifugal pump, not a dinky mag drive.

An accumulator is a vessel containing a rubber bladder that is pressurized with nitrogen or any inert gas. So water entering the accumulator compresses the bladder, giving you a cushion to pump against. It also absorbs the energy causing water hammer.

Now that Im thinking about water hammer, It wouldn't be an issue. Your pressure control valve would have to be downstream of the pump and upstream of the misters, and as long as its running the water could only move in one direction anyways.

redi jedi said:

In regards to dead heading, its not really about the heat. Its the fact that the pump is moving water but it has nowhere to go. Since water is not compressible the pump will either stall or start breaking vanes off the impeller. Note im talking about a centrifugal pump, not a dinky mag drive.

An accumulator is a vessel containing a rubber bladder that is pressurized with nitrogen or any inert gas. So water entering the accumulator compresses the bladder, giving you a cushion to pump against. It also absorbs the energy causing water hammer.

Now that Im thinking about water hammer, It wouldn't be an issue. Your pressure control valve would have to be downstream of the pump and upstream of the misters, and as long as its running the water could only move in one direction anyways.

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The way it should be done is pump then pressure relief valve then pressure switch then check valve then accumulator then solenoid valve then spray nozzle = correct system

pirateb0b said:

I understand the benefits of an accumulator - less wear on pump, stored pressure when power dies etc. However, I'm wondering if the main benefit of instant pressure to misters can be replicated by using a 100 psi (or other desired pressure) cracking pressure inline check valve.

Click to expand...

A check valve would only be worth having in-line if you have a problem keeping your pump primed.

We are using a 1/2 manifold with 45 nozzles and two $39 Shurflo 181-201 24 OZ accumulators. With dual Shurflo 125 PSI on demand pumps and the accumulator diaphrrams pumped to 85 PSI, we get at least two, sometimes three cycles at 3 seconds on before the pump has to recharge the system. The system never drops below 60 PSI and operates mostly between 125-80 PSI.

I just did a 400 hour record of electricty usage on two pumps powering 45 heads and it worked out to 0.0207 KWH every 24 hours. Or basically $0.75 a year in eletricity. Yep... $0.75 cents. That's moving about 8 gallons a day of water drain to waste in a 102 site system.

Slow motion video.... Videos are in HD.. so be sure to select it.

https://www.youtube.com/watch?v=w_6t1kevAMs

Prototype testing..

https://www.youtube.com/watch?v=ny4G5Ktm4L0

hammer21 said:

The way it should be done is pump then pressure relief valve then pressure switch then check valve then accumulator then solenoid valve then spray nozzle = correct system

Click to expand...

There is no need for a RV.. there is no saftey issue involved in Aeroponics. It's not like a hot water heater that will explode. Most diaphram pumps have a built in pressure switch. The only trick is making sure you pump your accumulator up to a pressure higher than the low side of the pressure switch.

indrhrvest said:

There is no need for a RV.. there is no saftey issue involved in Aeroponics. It's not like a hot water heater that will explode. Most diaphram pumps have a built in pressure switch. The only trick is making sure you pump your accumulator up to a pressure higher than the low side of the pressure switch.

Click to expand...

You are correct to a point about pressure relief valve. I use fat boy pumps with no relief valve or pressure switch. Found out long ago you should not trust pumps with these built in when banging over 80 psi my system is set at 110 psi to 115 psi and can run them at 150 psi if needed

indrhrvest said:

There is no need for a RV.. there is no saftey issue involved in Aeroponics. It's not like a hot water heater that will explode. Most diaphram pumps have a built in pressure switch. The only trick is making sure you pump your accumulator up to a pressure higher than the low side of the pressure switch.

Click to expand...

Its not about safety issues, the op is/was trying to find another means of building pressure without using an accumulator.

redi jedi said:

Its not about safety issues, the op is/was trying to find another means of building pressure without using an accumulator.

Click to expand...

You don't have to use an accumulator, but you can get shorter cycles with one. It also extends the life of the pump. There pretty much is no reason why you wouldn't want one. An accumulator doesn't build pressure, it stores it. So when your solenoid valve opens there is instant pressure. It takes a diapgram pump a few cycles to reach pressure, the accumulator simply provides pressure infront of the pump to aid the diaphgram in doing it's job.

I've tested a lot of pumps and you simply can't go wrong with the Shurflo pumps and accumultors for the price/value. Those fatboy pumps seem overpriced.

http://www.youtube.com/watch?v=x-VkmlwThD0

Just having a look at the spec for those inline check valves again, there's a graph that indicates if the cracking pressure is set at 100psi, flow would have to drop to around 70 psi - the 'resealing pressure' before it would close. Great way to put together a custom anti-drip nozzle - providing cracking pressure doesn't have a wide tolerance.