2" from skimmer, 1.5 back to pool..

[rcy]

Is there any reason my pool builder installed my lines this way. It's 2" from the skimmer to the pump, then 1.5 everywhere else. The dedicated suction line (for the Baracuda cleaner) is also only 1.5".

Thanks.

 

[stev32k]

That is actually good design. The larger line going to the pump reduces the friction loss and will result in more reliable operation. It is much harder for a pump to suck water than it is to pump it out. So inlet friction losses can cause problems with water getting to the pump which can mean loss of suction if the water level gets low. I would say your pool builder knows a little about hydraulics.

P.S. I did a little checking and to give an example of what I'm talking about the maximum flow for a 1.5" line should be about 60 gpm (225 L/min). At 60 gpm the friction loss in 1.5" steel pipe would be about 10 psi/100'. At 60 gpm the friction loss in 2" steel pipe would be about 3 psi/100'. The loss numbers for PVC pipe will be a little less than steel pipe but the difference in loss will be about the same. This difference can mean your pump will last (a lot) longer because of less cavitation, be much less prone to losing suction, and chances are you won't have to prime your pump when starting up.

 

[Onslow]

If his design were 2" all the way abound would that be better/worse?

Reason I'm asking: I'm getting ready to hard plumb and am considering all 2" PVC. This post has me wondering about that strategy.

 

[JasonLion]

Generally, using larger pipe everywhere is better, but using it some places is more important than others. There are lots of factors that enter into it. The more parallel runs between the equipment pad and the pool the less important larger pipe sizes are, since parallel runs are the same as a single larger pipe. Larger pipe is more important on suction than it is on the return. And a number of other progressively less important rules that can affect things in various situations.

 

[stev32k]

If his design were 2" all the way abound would that be better/worse?

Reason I'm asking: I'm getting ready to hard plumb and am considering all 2" PVC. This post has me wondering about that strategy.

The maximum flow and pressure requirements of your filter must be used along with system piping characteristics ie length, diameter, elevation, and number and type of valves and fittings to arrive at the system design. If your filter has a maximum flow rating of 60 gpm and max pressure of 50 psi then you don't need a pump that puts out 150 gpm and 100 psi. Basically the design needs to consider the system pressure loss at various pipe sizes and that will determine the pump requirements. As pipe size increase pressure loss will decrease (at constant flow) and pump head requirements will decrease. So it boils down to cost. If 1.5" pipe will satisfy system pressure requirements then the additional cost of 2" pipe is wasted money.

Pump suction piping should be handled differently and is dependent on the system layout. Improper suction piping is the most frequent cause of pumping problems. The best layout would have the pump suction below the normal water surface level. This would provide a positive pressure at the pump suction (flooded suction) . If the pump suction is above the surface level then the pump must be able to lift (suck) the water to the suction. If the suction pipe size is such that the pressure drop is right at or below the lift requirements of the pump the result can be cavitation, loss of suction, loss of flow, difficulty priming, and damage to the impeller. Even in a flooded suction installation the velocity of the water entering the pump should be between 3 - 6 ft/sec for horizontal end suction pumps.

Here is a link to a site that has all the information you need on piping systems: http://www.engineeringtoolbox.com/pipin ... s-t_6.html

 

[jcasper]

i also want to add a ???? to this as far as the water flow. im hard plumbing my set up this sunday and was going 1.5 but now seeing this im wondering about adding the suction side to 2". my ???? is if i do 2" want is still be like having 1.5" since i have to reduce it back down to a 1.5 going into the pump?

 

[stev32k]

i also want to add a ???? to this as far as the water flow. im hard plumbing my set up this sunday and was going 1.5 but now seeing this im wondering about adding the suction side to 2". my ???? is if i do 2" want is still be like having 1.5" since i have to reduce it back down to a 1.5 going into the pump?

Reducing or enlarging the pipe size at the pump inlet and/or discharge is very common and has little to no effect on friction loss. So yes, run 2" to the pump then use a 1-1/2" X 2" reducing adapter at the suction inlet.