New Pump Recommendations

[pool60]

How do you measure vacuum pressure? I want to figure out my "feet of head" at this site but don't know my vaccum pressure.

http://www.poolplaza.com/pool-pump-sizing-2.shtml

 

[pool60]

Well I bought a 3/4 HP full rated energy efficient Whisperflo. I'll let you know how things turn out.

 

[JasonLion]

You measure vacuum pressure with a vacuum pressure gauge, which unfortunatly is not a very common thing to find. The ones I have seen cost at least $100 and you will need adapters to make a good connection to your system. It is simpler to get a flow gauge, under $100 and more directly useful, though the two are not completely interchangeable.

 

[mas985]

You can use an automotive vacuum guage which Sears and other stores have for about $20.

 

[pool60]

How do I hook it into my system? How would I do the test? Is there a site that shows how maybe?

Thanks

 

[JasonLion]

One good place to attach a vacum gauge is one of the drain plugs on the pump. You will need to find the correct adapters for your pump/gauge.

The idea behind the test is to measure the vacuum pressure and the filter pressure at the same time while the pump is running, which will tell you the total dynamic head. See this thread for a through discussion and the equation to convert pressure to head.

 

[pool60]

Well I installed the Whisperflo 3/4 HP pump, but there's even more air under the glass than before. I think it's time to call somebody....

 

[JasonLion]

Air in the strainer basket is usually from a leak in the pumbing, though a low water level in the skimmer can sometimes draw in air. The O-ring on the basket lid is the first thing to check, though that should be fine on a new pump. Leaks on the suction side can be difficult to spot. Sometimes spraying things with shaving cream will show the leak (the cream will get sucked into the leak). Other times they are underground and very difficult to find. If you have more than one source, main drain and skimmer, more than one skimmer, etc, and valves to control each, you can try turning all but one off and see if the air is coming from a particular line.

 

[mas985]

If you have a blockage in your suction line, it will also cause air to accumulate in the pump basket. The 3/4 HP Whisperflo is a very powerfull pump and may be too powerful for your plumbing. In reality it is a 1.2 BHP pump. If the suction gets too high, the pump will pull air in from almost anywhere and it doesn't matter if the seals are good or not.

As Jason pointed out, first check for leaks. Then I would check for any blockage in the lines. Use a drain king to back flush the suction line. If you cannot find any leaks and the lines are clear, it could just be over dimensioning of the pump.

Based upon the info you gave earlier on your plumbing, here are some estimates (my best guess) for the current pump and plumbing:

Suction Head loss: 19 ft. (very high and could cause air to be sucked in)
Return Head Loss: 26 ft. (fairly low compared to suction)
Filter PSI: 11
GPM: 75

A balanced system will have return head that is at least 3x that of suction head. Yours is less than 1.5x which means your suction head is a bit too high.

Did you ever replace the filter guage? If so, what is it reading now?

 

[pool60]

The filter pressure is 14PSI. It was 9 PSI before I put the new pump on.

 

[mas985]

The numbers I quoted were for 2" plumbing but I went back and noticed that you posted it was 1.5" plumbing, my bad. So here are the numbers for 1.5" plumbing.

Suction Head = 39.8 feet
Return Head = 32.7 feet
Total Head = 72.5 feet
Flow = 43.9 GPM
Filter Pressure = 14.2 PSI

Initially, the model predicted 16 PSI filter pressure using baseline assumptions so I had to add a lot of suction head to bring it down to 14 PSI. You will notice that the suction head is higher than the return head which is not normally the case for pool plumbing. The imbalance is very high so I strongly suspect that there is some sort of blockage in the suction line to cause this high of head loss. This would also explain the air in the pump basket. Try flushing out the suction line and see if that helps at all.

 

[pool60]

How would I flush out the suction line? Thanks for your assistance. I really appreciate it.

 

[JasonLion]

To flush the suction line you want to run water from the pump back to the skimmer. Usually you can remove the pump strainer basket and get a garden hose fitted with a drain king into the intake pipe. Then turn on the garden hose and run water into the pool through the skimmer. If you have more than one skimmer/main drain and valves on each of them try running water to each one seperately. If you do flush something out it can sometimes make a little bit of a mess in the pool, though sometimes you can catch it in the skimmer.

 

[pool60]

Oh okay. That's simple. I'll do it this afternoon. I have one skimmer and three jets.

Do you think it's okay to run the pump with air bubbles in the line? Also, I'm worried that the pump is too strong. It's coming out of the jets about twice as strong as before. It's actually creating ripples across the whole pool.

Is it too much pressure for the pipes? My biggest fear is that there's a leak underground somewhere. I know that would cost an arm and a leg to fix. They'd have to tear up some concrete to get to it.

 

[JasonLion]

Pipes can handle very high pressures if properly installed. What does the pressure gague on your filter read?

A little air in the line won't bother anything. You may need to manually bleed air out of the filter occasionally, though some filters do this automatically. Too much air and the pump can lose prime and the filter can fill with air, which makes filtering very inefficient at best.

 

[pool60]

The pressure is 14 PSI on the pump. The filter is working great! The water is clearer than ever.

 

[Rangeball]

pool60, in the past, I've had issues with air leaks in the supply valves ahead of the pump. Replaced the valve, no more leaks.

Something else to check?

 

[JasonLion]

At 14 to 25 psi your pipes are going to be just fine. I wouldn't have any worries about pressure below 40 psi. Most of the plumbing is probably designed for 100 psi, and even some of the lower pressure components are still probably going to be rated for 50 psi or better. In the range you are talking about "too big a pump" is more of an aesthetic and electric cost issue than any material risk.

 

[pool60]

That's encouraging to hear. I was totally bumbed when I first powered it on and saw the bubbles and saw the big increase in pressure. My old pump was 1 HP with SF of 1. This new one is 3/4 HP with SF of 1.67. I'm assuming the new one will use more electricity, right?

I'm going to try using the shaving cream on my pipes too.

 

[mas985]

My old pump was 1 HP with SF of 1. This new one is 3/4 HP with SF of 1.67. I'm assuming the new one will use more electricity, right?

Energy use is approximately proportional to BHP so, the pump energy consumption will go up by about 25%. However, because the flow rate is higher (~20%), your turnover is shorter so you could reduce run time by the same amount and come out about the same. The Whisperflo is more efficient than your old pump so I believe you will come out ahead.