# New Equipment TDH Calc - Am I way off?

#### julietalpha

##### Member
HI everyone. New pool and new equipment. Pump is Hayward TriStar VS SP3202VSP. I'm trying to get accurate TDH calculations so I can properly configure this to be energy efficient.

I picked up a vacuum gauge and a pressure gauge and hooked them up to the pump ports and got the following readings. I'm just not sure my vacuum readings are accurate, as they seem extremely low. Plumbing is 2.5" suction and 2" returns. Pool / Spa combo. Do these seem reasonable?

Pool/SPA Mode
3450 RPM = 4 in hg / 17 PSI (TDH 43.79 after 1.13 / 2.31 multipliers)
3000 RPM = 3 in hg / 14 PSI (TDH 35.73 after 1.13 / 2.31 multipliers)
2400 RPM = 1 in hg / 9 PSI (TDH 21.92 after 1.13 / 2.31 multipliers)
1725 RPM = 0 in hg / 5 PSI (TDH 11.55 after 1.13 / 2.31 multipliers)

SPA ONLY Mode
3450 RPM = 4 in hg / 23 PSI (TDH 57.65 after 1.13 / 2.31 multipliers)
3000 RPM = 3 in hg / 18 PSI (TDH 44.97 after 1.13 / 2.31 multipliers)
2400 RPM = 1 in hg / 12 PSI (TDH 28.85 after 1.13 / 2.31 multipliers)
1725 RPM = 0 in hg / 6 PSI (TDH 13.86 after 1.13 / 2.31 multipliers)

Thanks for any info!

#### Jimrahbe

TFP Expert
Julie,

For the life of me I can't figure out why anyone would care about TDH???

What is it that you are trying to do?

If you have a VS pump you want to run it as slow as you can to get the job done.. Since you do not have a SWCG, your low speed would be what it takes to make your skimmers work well.

In my case, I run mine at about 1200 RPM about 90% of the time..

Let's see what @mas985 has to say..

Jim R.

#### JamesW

TFP Expert
I would say that the numbers seem reasonable. How many suction lines are open during the test?

2.5" suction plumbing indicates that the builder is probably smarter than most.

At 44 feet of head, the flow rate will be about 105 gpm.

Speed......feet.....gpm
3450.........44.......105
3000.........36.........90
2400.........22.........65
1725.........12.........45

As noted above, the best way to operate is to run as slowly as possible.

For skimming, you just need enough flow to get visible movement in the skimmer.

For a SWG, you just need enough flow to close the flow switch plus about 200 rpm for margin.

For a gas heater or solar, you need about 40 gpm

When running the heater, try to get about 40 to 45 gpm. Otherwise, go as slow as possible.

I would suggest 2,400 rpm for heating and 1,200 to 1,400 when not heating.

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#### julietalpha

##### Member
Julie,

For the life of me I can't figure out why anyone would care about TDH???

What is it that you are trying to do?

If you have a VS pump you want to run it as slow as you can to get the job done.. Since you do not have a SWCG, your low speed would be what it takes to make your skimmers work well.

In my case, I run mine at about 1200 RPM about 90% of the time..

Let's see what @mas985 has to say..

Jim R.
I'm simply trying to get an accurate flow rate by utilizing TDH. I want this data so that I can set my VSP schedule with some level of efficiency.

I would say that the numbers seem reasonable. How many suction lines are open during the test?

2.5" suction plumbing indicates that the builder is probably smarter than most.

At 44 feet of head, the flow rate will be about 105 gpm.

Speed......feet.....gpm
3450.........44.......105
3000.........36.........90
2400.........22.........65
1725.........12.........45

As noted above, the best way to operate is to run as slowly as possible.

For skimming, you just need enough flow to get visible movement in the skimmer.

For a SWG, you just need enough flow to close the flow switch plus about 200 rpm for margin.

For a gas heater or solar, you need about 40 gpm

When running the heater, try to get about 40 to 45 gpm. Otherwise, go as slow as possible.

I would suggest 2,400 rpm for heating and 1,200 to 1,400 when not heating.
JamesW, thanks for the information. With the "SPA+POOL" numbers provided, I have the main drain open at 25% (2 drains connected to one line), skimmer open at 75%. With SPA numbers, only the SPA drain is open at 100%.

Again, just trying to get flow rates down so I can be economical.

#### JamesW

TFP Expert
Ok, seems like you have a pretty good understanding of what you're doing.

I think that the speeds that I indicated should work for you.

I would leave the skimmers open 100% all the time and the main drain about 10 to 15% open.

TFP Expert