One Inlet, Two Pumps, Two Outlets and a Headache

[cottora]

Hi! I recently purchased a home that came with an in-ground spa:

1500 Gallons
A small two feet tall 30 GPM Waterfall (that is currently being blasted at over 100GPM)
Jets and Blower
Hayward Heater
24" Hayward Sand Filter (filter is cracked and needs to be replaced)
2HP Motor (way, way overkill)
Diversion Valve for Waterfall or Jets (or Combination)
System about 30' from pool

Here is my issue, my wife really wants to run the waterfall during the afternoon for aesthetic purposes. However, I dont want to pay to run a 2 HP pump for something a 1/2 HP could handle.

I am in the power industry and know just enough about pumps to know I can screw things up, so I wanted to get some pros advise on the below idea:

Reroute the 2HP pump to operate the jets only
Install a small pump/sand filter that is routed to the waterfall only (will run every day to turn/filter water and give us a waterfall)

Questions:
Can I use a single 2" supply line to run two mismatched pumps?
Also, all of the filters that are the size I want have gravity fed pumps. My system is installed next to a wing wall so getting water gravity fed to the inlet would not be an issue.
But can I run a 2HP pump with a small gravity fed pump on the same inlet line?
What happens when someone accidentally turns both pumps on?
Assuming we make it to this question, is there any issue using an "above ground" filter/pump in an inground pool (keeping in mind that I can gravity feed the pump)

Thanks in advance!

 

[jblizzle]

Welcome to TFP!!!

I think the simplest solution would be to put a 2-speed motor on your pump (or just replace it with a new 2-speed pump). Then run on low for filtration and waterfall, then switch to high speed when you want the jets.

Filters and pump are separate pieces of equipment ... you do not have to buy them in a combo unit.

 

[cottora]

Thanks, I appreciate the quick reply!

Here is the thing, I have to replace the sand filter. It would be less expensive if I can get a smaller filter/pump that is sized right as opposed to replacing the working pump with a two speed and still having to buy a sand filter. Plus, I am not a fan of two speed pumps for efficiency reasons.

My thinking is I could put check valves at each pump's intake so they dont "fight". But I am not sure they would fight to begin with...

 

[jblizzle]

Well, if you think it is more cost effective to have 2 pumps and are able to modify the plumbing then fine. You likely would be better off having the jet pump bypass the heater and filter completely and then use the smaller pump/filter for circulation, filtration, heating, and the waterfall. But this may not be possible depending on how your hot tub is plumbed.

Your efficiency argument against 2-speed does not make sense to me since a 2HP on low speed will still use less power than a single speed 3/4-1HP pump.

 

[cottora]

Sorry, I am thinking about throttling instead of two speed. But how about the below questions:

Can I run a 2HP pump with a small gravity fed pump on the same inlet line (I am thinking a check valve would be necessary)?

What happens if someone accidentally turns both pumps on?

Assuming we make it to this question, is there any issue using an "above ground" filter/pump in an "in-ground" spa (keeping in mind that I can gravity feed the pump)?

 

[jblizzle]

Can I run a 2HP pump with a small gravity fed pump on the same inlet line (I am thinking a check valve would be necessary)?

Honestly, I am not sure. Having 2 pumps on the same suction line could work (with check valves), but may cause problems if both were on at the same time (which is what I was suggesting would be best if the jet pump was not used for filtering and heating ... but this is usually done with separate suction lines)

What happens if someone accidentally turns both pumps on?

I am thinking that the 2HP may pull such high suction that the small pump may not be able to pull enough to open the check valve ... might run the small pump dry. I am totally speculating here.

Assuming we make it to this question, is there any issue using an "above ground" filter/pump in an "in-ground" spa (keeping in mind that I can gravity feed the pump)?

Should be fine as long as gravity fed for priming.

 

[cottora]

Thank you!

We have the same concern regarding running the pumps at the same time.

Not that I am going to do this but...I thought about running a small slip line from the 2HP pump outlet to between the small pump and the small pumps check valve. This would supply water so the pump does not run dry but I imagine it could cause a whole host of other issues. Could potentially do the above setup and not install any check valves...

 

[jblizzle]

But then the 2HP may pull water backward through the small pump if you do not use check valves.

Still seems easier to go with a new 2-speed motor, but understand you concern that it is currently working fine. One issue with keeping the large pump would be that you should not go smaller on the filter or the pump will be too powerful for the filter on high speed.

 

[Cloudbusting]

Get a variable speed pump, you might be able to run the waterfall at 1500rpm / 150watts - saving you 90% while getting a $500 credit from some DWPs

 

[jblizzle]

How close to the drain could you attach a second suction line? If you are able to get pretty close, then the likelihood of pulling water from the other pump is lower as it should be less resistance to pull from the drain.

In your original proposal, which pump would be running through the heater?

 

[jblizzle]

Get a variable speed pump, you might be able to run the waterfall at 1500rpm / 150watts - saving you 90% while getting a $500 credit from some DWPs

That would only really make sense if you had expensive power and a large rebate from the power company. Although one of the smaller VS pumps could be a good option if you get a rebate.

 

[cottora]

VS Pump is not in the budget...

How close to the drain could you attach a second suction line?

I cannot get close because of concrete work. The pumps would be close to each other.

In your original proposal, which pump would be running through the heater?

I want the new filter to be sized with the new pump. Essentially I am completely separating the system as follows:

2HP Pump to Heater to Jets

1/2HP Pump/Filter System to waterfall

BUT, they both share a 2" inlet line that I will tee-off for the small pump

 

[mas985]

Can I run a 2HP pump with a small gravity fed pump on the same inlet line (I am thinking a check valve would be necessary)?

Yes but I am with Jason on this, I think you would be better off with a single two speed pump. You could just build in a partial bypass around the filter to limit the flow rate through the filter. Also, you don't want full flow going through the heater either so I would bypass that too.

What happens if someone accidentally turns both pumps on?

The suction head would increase with both pumps running and perhaps increasing the likely hood of an air leak or worse it might force either pump to cavitate.

Assuming we make it to this question, is there any issue using an "above ground" filter/pump in an "in-ground" spa (keeping in mind that I can gravity feed the pump)?

So the pump will be below the spa and pool water level?


Also, are you sure that the waterfall can get away with a lot less flow rate? It might turn it into a dribble rather than a fall.

 

[cottora]

I agree that a two speed is a better setup. However, buying a two speed pump is more expensive than a small filter/pump combo. Plus, I would still need to purchase a filter. A new two speed and filter is about $900 if I size the filter for the high speed. If I size the filter for the low speed it may save me $200 but I risk accidentally running the filter on high.

I can get small pump/filter for around $350.

So the pump will be below the spa and pool water level?

Correct

Also, are you sure that the waterfall can get away with a lot less flow rate? It might turn it into a dribble rather than a fall.

Good point, I choked the flow to the waterfall down to 25GPM (tested with the 5 gallon bucket and stopwatch method). 25GPM was sufficient. 30-40GPM was perfect. Currently the dang thing shoots to the other side of the spa...

 

[jblizzle]

At some point you have to pay to play. Try to cut corners / save money up front and possibly have problems in the future. Or do it right the first time.

With some creative plumbing, you could add a bypass around a smaller filter. Have a valve that selects between the filter and waterfall OR the heater and the jets. Then have a manual switch for the pump speed ... so you always are there and can switch the valve and the speed at the same time.

That really is the cleanest route forward, maybe not the cheapest.

You could look at a smaller 2-speed motor with a smaller impeller to be used with your existing pump. Or find a 2HP 2-speed motor and use the existing pump and impeller.

Or take a chance and see if you can get a small combo filter/pump unit to work and hope you do not have to try to sell it used for a loss.

 

[mas985]

At some point you have to pay to play. Try to cut corners / save money up front and possibly have problems in the future. Or do it right the first time.

My mother use to say: "Penny wise, pound foolish"

I agree that a two speed is a better setup. However, buying a two speed pump is more expensive than a small filter/pump combo.

Not if you just replace the motor. It shouldn't be much more than an AG pump. What is the current pump model?


But if you insist on your madness, then the only safe installation of the two parallel pumps would be to use a check valve on both pump outlets and to wire the pumps so that they cannot be turned on at the same time (i.e. two speed DPDT switch or timer).

 

[cottora]

Thank you for the reply!

use a check valve on both pump outlets

Would it be better to have the check valves on the inlet side or outlet side of each pump?

 

[CUTiger78]

You know, it sounds like you're proposing a setup similar to a typical pool w/ a pressure side cleaner (like a Polaris 380) setup. The only change it that instead of running a Polaris, you'll be running a waterfall.

Here's my setup: Water from 2 suction lines (skimmer/main drain combo & another skimmer) feeds a 1hp Hayward Superpump. From the pump through a 24" Hayward sand filter out through a gas heater and back to the pool returns. The return line has a T after the heater. One line out of the T goes directly back to the pool; the other goes to a .75hp pump that feeds a dedicated return line for the Polaris.

The 1hp pump has to be running to feed the .75hp pump. The .75hp pump has a check valve and can be totally isolated if necessary. My setup is totally manual, so I know not to run the small pump unless the big pump is on.

So, for your waterfall & gravity-fed pump, maybe you could cut in the new pump at the "diversion valve." It should work fine when both pumps are on, but I don't know how a "gravity-fed" pump would work if the main pump isn't running.

Just my $.02. Good luck!

 

[jblizzle]

But that assumes you would be running the large pump to feed the smaller pump from the return line which is not what cottora is trying to do. Plus I am not sure the waterfall pump would be designed to be fed pressurized water like that.

 

[mas985]

Would it be better to have the check valves on the inlet side or outlet side of each pump?

The effect is the same which is to eliminate re-circulation losses, however, for pumps you are much better off adding head loss on the return side than the suction side.

Also, the reason cleaner booster are plumbed in series is because they need higher pressure. Series plumbed pumps add in head while parallel pumps add in flow rate. So I would only plumb a pump in series if you are going to run both pumps at once and need a very high head output which is not the case here.