Cycle Stop Valve

Discussion in 'Open Loop' started by ldameron, Mar 4, 2009.

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1. ValvemanGuest

A two pump system would save a lot of energy over a single pump with a VFD or a CSV. However, I will try to figure a one pump system to handle everything. I cannot get efficiency curves for 4" submersible pumps. I would like to post a curve below by Grundfos Pump Company that they made to explain the differences between VFD and CSV. They used a 10 HP pump at 231' of head. We can use this curve to figure the difference of power in percentage, and scale down to a 2 HP, which is what it would take for the system you describe.

Using CSV;
This curve shows 10 HP required for 105 GPM at 231' at 3450 RPM.
At 2/3rds flow 8 HP required for 70 GPM at 231' at 3450 RPM.
At 1/3rd flow 5 HP required for 35 GPM at 231' at 3450 RPM

Using VFD;
At full flow 10.5 HP required for 105 GPM at 231' at 3450 RPM.
At 2/3rds flow 7.7 HP required for 70 GPM at 231' at 3163 RPM.
At 1/3rd flow 3 HP required for 35 GPM at 231' at 2886 RPM.

Full Flow;
CSV 100% of HP
VFD 105% of HP

2/3rds flow;
CSV 80% of HP
VFD 77% of HP

1/3rd flow;
CSV 50% of HP
VFD 30% of HP

Using a 2 HP submersible to produce 1/3rd flow of 10 GPM for 4,000 hours at .10 per KW.
CSV \$459.00
VFD \$276.00
Difference of \$183.00

2 HP submersible to produce 2/3rds flow of 20 GPM for 2,000 hours at .10 per KW.
CSV \$368.00
VFD \$354.00
Difference of \$ 14.00

2 HP submersible to produce full flow of 30 GPM for 500 hours at .10 per KW.
CSV \$115.00
VFD \$121.00
Difference of \$ -6.00

Total difference of \$191.00 per year or \$15.91 per month. Figuring a VFD for a 2 HP at about \$1,000.00, that would be more than a 5 year pay out. If the VFD last longer than 5 years there are some savings. If the VFD last less than 5 years, you never break even.

The CSV has proven to increase the life of pump systems.
The VFD has proven to shorten the life of pump systems.

I got the cost per KW form this web site;

http://www.productiveenergy.com/calculator/pump.asp

Which is also where I got this interesting quote.

“Energy savings for your system may be toward the low end of the above range, but don't forget that usually the energy savings are often small compared to production benefits of having a more reliable system. If the potential savings are towards the low end of the scale, you may not be able to afford pricier optimization options like Adjustable Speed Drives.”

There are many variables such as hours of operation, percent of flow, price per KW, and cost of equipment. When the required flow rate is small the majority of the time the VFD does slightly better. When the required flow rate is high most of the time the CSV does better. When the flow rate is low half the time and high the other half, it is a wash between CSV and VFD. The largest savings are usually in making the equipment last the longest.

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2. ValvemanGuest

I think it is funny that you chose a demand that required a 2 HP submersible. I was just about to post this anyway. It gives further proof of what I said above.

The following pictures are of an impeller/diffuser, and motor thrust bearing from a 2 HP submersible pump. This was an accelerated test to see how Cycle Stop Valves affect pumps and motors. This pump was actually in the well for over 12 years. During that 12 years, we accelerated the work on the system to simulate a pump system with over 30 years of service.

This pump ran for several years at only 1 GPM. It also ran for several years at varied flow rates from 2 to 25 GPM. All of this time it also supplied two houses with a pressure tank that only held 2.5 gallons of water. So it was also allowed to cycle on and off for intermittent demands. In 12 years we did everything we could think of to try and destroy this pump.

The pump was finally removed for inspection and the following was observed. There is absolutely no down thrust, upthrust, or radial damage to the impeller, diffuser, shaft, or bushings in the pump. The thrust bearing in the motor still looks like brand new, and the motor windings tested and looked perfect.

The average life of previous pumps in this test well was less than 2 years. The CSV made this pump last 6 times longer than the average, and it would still be working today if we had not disassembled it for inspection. After inspection, I see no reason this pump would not still be just as good in another 12 years, or even another 24 years. I probably would not be around to see how long it lasted.

Pump and motor companies know that the CSV makes pumps last longer and use smaller tanks. This is exactly why they promote VFD systems and discredit the CSV at every opportunity. Having a pump that outlast several generations is real savings, in energy and in dollars. Pump and motor companies are not going to advocate the use of a Cycle Stop Valve, anymore than an oil company would advocate a device that makes a car get 200 MPG, or a car company advocate a car designed to last 20 years or more.

As you can see from these pictures, the wearable parts of this 12 year old pump and motor still look perfectly new. This is proof that the Cycle Stop Valve makes pumps and motors last longer.

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3. GuestGuest

Those are excellent posts.

Let's see if I can argue some of the other side. I agree that a two pump system makes the most sense - why pressurize everything to 60 psi when most of your usage only needs 20 psi.

Some of the head has to be due to frictional losses and this factor helps the VFD numbers.

I agree that 2 HP is about right and power usage, electricity cost and savings are right.

I do see VFD drives that can be added to any 3phase pump for \$300, but it is not clear to me if these could be made to work (would at least need a pressure sensor).

I consider 5 year payback on saving energy pretty good.

While I don't doubt that a CSV pump can last a long time, I'd like to see more support for it lasting longer than the pump with a VFD. I would expect the all electronic VFD itself to last a long time. Looks like lots of commercial systems are going to VFD.