# Thread: Vacuum Pressure and Filter Pressure

1. ## Vacuum Pressure and Filter Pressure

Vacuum is 14" Hg (at pump drain) ~ 15.82 psi
Filter Gage is 12 psi

I have (2) 1-1/2" going into 3 way Jandy and 2" going into the pump
1-1-2" going into the pool (3 eyeballs) Heater and filter is 2" in/out.

How would I figure my head ??

2. ## Re: Vacuum Pressure and Filter Pressure

14 inches of mercury is 6.876 psi or 15.86 feet of head. 12 psi = 27.68 feet of head. Your total head loss is 15.86 + 27.68 = 43.54 feet.

You can add the height of the pressure gauge above the suction gauge for a more accurate number.

What pump do you currently have?

3. ## Re: Vacuum Pressure and Filter Pressure

No name on the pump, but motor is 1 hp. So total should be about 45 ft. is that good or bad

4. ## Re: Vacuum Pressure and Filter Pressure

45 feet is well within the normal range. How good or bad that is depends on what you are comparing to. That is perfectly fine for a random pool, not so good if you had an efficiency expert design everything.

5. ## Re: Vacuum Pressure and Filter Pressure

I have ordered (latest & greatest) new Pentair VS (8 speed). Any heads up ?

6. ## Re: Vacuum Pressure and Filter Pressure

That is a great pump. The main thing to keep in mind is that it is a fairly complex piece of technology. It will work right out of the box, but to take full advantage of it, you should plan on spending some time getting things optimized.

7. ## Re: Vacuum Pressure and Filter Pressure

sukhbir, it's important to understand that that head loss is only for that flow rate. Every flow rate will generate a different head loss. If you plot these numbers, you will create a "System Curve".

A system curve is like a pump curve. To get your system curve, you would use different flow rates and note the vacuum and pressure.

8. ## Re: Vacuum Pressure and Filter Pressure

Here is my plan
Hook up the vacuum gauge to pump.
Clean the filter.
run pump and record rpm,filter pressure, vacuum, watts
rpm will be 3450,3000,2800,2400,2000,1600,1200,800, and lower if worked
and post them here. How can I figure the GPM ?
Anything else I should do ?

9. ## Re: Vacuum Pressure and Filter Pressure

But for most plumbing, if you have the flow rate at one speed you can just scale the flow rate by RPM.

GPM New = GPM Old * RPM New / RPM Old

However, check valves can through this off some.

The problem with measuring pressure and vacuum at low speeds is the resolution is not very good so the measurement error is high. So you are better off calibrating at high speed and scaling for lower speeds.

10. ## Re: Vacuum Pressure and Filter Pressure

Thanks Mark will do

11. ## Re: Vacuum Pressure and Filter Pressure

I just uploaded a new version which can be calibrated with your pressure and vacuum measurements at high speed. The tab is called Head2GPM.

12. ## Re: Vacuum Pressure and Filter Pressure

Just Did. and #s are really close what I am expecting. Now let's see how the real life looks like. Thanks again Mark

13. ## Re: Vacuum Pressure and Filter Pressure

You could use a flowmeter to measure the flow rate.

That pump might be too much for your system at high speed, so be careful at the higher speeds.

14. ## Re: Vacuum Pressure and Filter Pressure

Originally Posted by sukhbir
No name on the pump, but motor is 1 hp. So total should be about 45 ft. is that good or bad

45' seems reasonable, but 14" HG seems high.

Typically on design we want no more than 10" HG max ~5" or less is ideal.

15. ## Re: Vacuum Pressure and Filter Pressure

This pool was built in 1983. One skimmer one main drain. both 1.5 dia into Jandy and 2" going into pump. 2" tee and 2 " from Spa. After heater 2" into spa and 1.5" to pool (3) 1" eye balls. ABout 70 ft from main drain and 36 ft from skimmer. about 1.5 ft above water level.
@racket Can I do something cheap to improve suction ?

16. ## Re: Vacuum Pressure and Filter Pressure

For dual 1.5" lines, that does seem a little high. What is your current pump? Are you sure both lines are clear and the valve is set to draw from both?

17. ## Re: Vacuum Pressure and Filter Pressure

No name on the pump but motor is 1 hp. Can't tell if both are fully open or not. Right now the way 3 way Jendy is plumbed is 2" from spa and 1.5" from skimmer and 2" going to pump. Main drain is plumbed into 2" to pump with a 2x2x1.5 tee. I can not control flow between skimmer/main drain. Main drain may be clogged. This pool was built in 1983.

My new plumbing plan is
skimmer(1.5") and main drain (1.5") into Jendy and 2" to the pump. Tee of the 2" to pump to 2x2x2 with 2 way jendy from spa. Replacing tees to 45 hope that will help the suction head and I will have more control over skimmer/Maindrain.

18. ## Re: Vacuum Pressure and Filter Pressure

If you are planning to cut into the lines, that would be a good time to use a drain king to flush the lines out and check for any clogs. Also, if you are replacing a 90 with 2 45's that may actually increase your head loss and decrease it so I wouldn't bother with that.

19. ## Re: Vacuum Pressure and Filter Pressure

Thanks Mark.

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