2 VSF Pumps on Common Suction Header?

[Jeff_TX]

Looking to replumb my entire equipment pad. Can I put two Pentair VSF pumps on a Common Suction header(Skimmer & Drain)? Each pump will have a suction side Flow-Vis Check Valve. One pump is the main pump serving Pool/Spa, Filter, Heater, SCG and return lines. The other pump is for water features only. Am I correct to assume if the pumps are operating at different speeds there will still be flow through the lower speed pump?

Jeff

 

[Jimrahbe]

Jeff,

You never connect two pumps to the same water source at the same time...

I would run the main pump off of the skimmer and then the water feature off of the main drain.

Maybe I just don't understand what you are planning to do???

Thanks,

Jim R.

 

[Jeff_TX]

Trying to have the ability to run desired water features while in spa mode, the typical pool/spa plumbing arrangement does not allow this. My sketch is attached. The header itself where both pumps take a suction from will need to be 2.5" pipe, skimmer and drain lines are 2".

 

[JamesW]

While the main pump is in Pool mode, you can use the main pump return for the water features.

While the main pump is in Spa mode, you can use a separate feature pump for the pool water features because the three-way valve is separating the pool suction from the spa suction.

Put a Jandy check valve at the discharge of the feature pump so that the main pump does not force water backwards through the feature pump when it’s off.

Note that laminars and sheers typically require a filter to prevent debris from clogging the features.

 

[Andrew_D]

As long as there is sufficient water availability, there should be no issue.

The problem would be if suction valves were closed (by accident or on purpose) so that only 1 suction point was bringing water to the pumps. Size of the pumps would also play a factor in this.

If we assume that each pump is using the full flow from a 1.5" line, then the 2 pumps would need a single 2.5" line all the way back to water. Also keep in mind that if the suction point is a skimmer, that the suction of the pumps isn't so great that air is pulled down in to it.

You had mentioned using 2" into the pumps. If the pumps are large enough that they need that full 2", then the header and piping back to the suctions (and the suctions themselves) would need to be 3".

Flow is related to many things, including number of fittings. That's why determining head is sometimes difficult. If simply comparing 2 pipes of the same length, flow is related to cross-sectional area. Just remember that Area is related to the Diameter squared.

So 1 pump pulling from 1.5" -> 1.5 ^ 2 -> 2.25.
2 pumps would double that to 4.5.
So can you use 2" for the header?
No, because 4.5 is bigger than 2^2 (4). So you would need to go up another size to 2.5" (2.5^2=6.25) for the header. (And all suction lines since it is possible to have valves set to only pull from one suction point.)

If the pumps need a 2" pipe, then they are each pulling from 2^2 = 4.
2 pumps => 4 * 2 = 8
So you would need 3" header and suctions since 3^2=9.

Proper calculation using the fittings will give a more correct answer. However, for long runs of pipe and minimal fittings, this will be close. Also, it depends if the pumps are running close to the max flow of the pipe size.

Andrew

 

[JamesW]

I would not put two pumps on a common suction line.

 

[Jeff_TX]

Good feedback, thank you. The numbers next to the lines are pipe sizes. 2" from skimmer and drain. I am stepping up to 2.5 for the "Common Header". The darkened valves are automated. When in Spa mode there should be no issue. Was trying to keep from running main pump at high speeds for the features. I have a separate cartridge filter for the Features.



Would this double the automation, since the features would need to know which pump is supplying flow?

Jeff

 

[JamesW]

Was trying to keep from running main pump at high speeds for the features.

What's the difference between running a separate pump or running the main pump a little bit faster?

How much flow do the features require?

 

[Jeff_TX]

Sheers, Bowls & Jets around 120 GPM. Which is more than I want to run through the filter, heater and salt cell. Revised schematic, this does allow the main pump to flow to the features. I guess that would help with freeze protection. Although most of the features I'll blow down with air to winterize.

Jeff

 

[JamesW]

You want to pull 120 gpm with the feature pump and 40 gpm with the main pump from the same suction?

That's not going to work.

Your suction is not adequate to do what you want.

The pool was not designed or built correctly to do what you want to do.

 

[JamesW]

Sheers, Bowls & Jets around 120 GPM. Which is more than I want to run through the filter, heater and salt cell.

You can do a 5 psi spring check valve bypass around the heater and cell.

You can replace the existing filter with a 520 square foot cartridge filter so that it takes the full flow.

Flo Control Valve, Check, 2 In, 5 Lb Spring (1095-20) - INYOPools.com

1095-20 - VALVE, CHECK, 2 IN, 5 LB SPRING (1095-20)

www.inyopools.com

In Spa mode, you can use the feature pump and pull from the pool suction and then go through a filter to the features.

In Pool mode, you can use the main pump at higher speed. The spring check valve will stay closed at low speed and it will open at higher speed so that you limit the flow through the heater and cell.

You can put a check valve at the discharge of both pumps to prevent backflow.

 

[Jeff_TX]

Ok, I need to expand on my desires.
Normal day to day operation is the main pump through the filter and back to the pool, maybe 1 feature(suction side 2x2" which is equivalent to 2.78" pipe, almost 3"). In "Party" mode the spa will be running through the main pump, filter, heater, salt cell and back to the spa(2x2.5" suction lines). In Party Mode all the "Bells and Whistles" need to run off the Feature Pump. 2x2" suction pipe should allow for enough flow for Main Pump filtration(2" line) and some flow through feature pump(2" line). My concern is the pump running at the higher flow will rob the available NPSH for the slower running pump. Maybe I need to run them at the same speed and "divert" some excess discharge flow from the feature pump to the main stream?

Jeff

 

[JamesW]

You really shouldn't try to run both pumps from the same suction.

You will not be able to balance the flow correctly.

For suction, you want to keep the water velocity below 6 ft/sec. For returns, you want to keep the water velocity below 8 ft/sec.

Size.......6 ft/sec......8 ft/sec.

1.5"...........38...............51 gpm
2"..............63...............84 gpm
2.5............90.............119 gpm
3.0".........138.............184 gpm
4”...........234.............313 gpm

Each suction pipe can supply 63 gpm for a total of 126 maximum available flow.

My previous post describes how I think that it can work.

 

[JamesW]

To do what you want with features, the pool should have had 2 skimmers for the main pump and a single "unblockable" or a set of main drains rated for at least 160 gpm and a 3" suction pipe feeding the feature pump.

Based on the current design and construction, you are at a significant disadvantage in trying to accomplish what you want to do.

 

[Jeff_TX]

Thank you James.
Features aren't set in stone yet. I need to shallow the deep end, rework the spa, replace the lights, new coping, tile, finish and finally, replace the equipment. The pool is currently 30,000gals and should be around 25,000gal when complete. I was trying to determine my feature capability based on: Converting the pressure side cleaner 1" line to a feature supply line, modify the 2 overflow features on the 1.5" line and potentially run an additional 2" line for any feature that required more water. The pool used to have 3 pumps. One each for the filter and spa with a booster pump for the Polaris(Replacing with a bot). Currently there are 2 skimmers and 1 drain(need to upgrade to 2) and I want to locate where they tie together, split them and route an additional line back to the pad. Granted, I'll need to remove some deck. I am familiar with the flow tables.

Recent Purchase:
Pentair: i10PS Intellicenter Load Center w/Comm card(will add 522038Z valve expansion card if required), IC40 Cell, 4 intellivalve controllers, 2 Intelliflo VSF pumps(011056), Quad DE 100 filter.

Jeff