Vertical Turbine Pump in a Wet Well

[ryano669]

We are trying to properly size the sump for a vertical turbine pump taking suction from a pond. The sump will have a straight channel approach. NFPA 20 states that the sump should be sized in accordance with the Hydraulics Institute Standards for Centrifugal, Rotary, and Reciprocating Pumps. Does anyonw have access to this standard, or experience sizing such a well? Thanks in advance.

 

[Pumpsonly]

You can purchase a copy from the Hydraulic Institute.

 

[Lan123]

What will be the anticipated maximum pumping rate?

 

[ryano669]

This particular application would be a maximum of 3000 gpm, but I would love to know how to calculate for future applications where the flow rate may differ.

 

[SprinklerDesigner2]

I've always followed the guidelines in NFPA 20 contained in the appendix always adding generously because it is cheap insurance.

The least expensive wet well to build is formed using standard 4' frames which result in all my wet wells being 4'x4'. With a smaller pump, a 250 or 500 gpm for example, a smaller wet well could be used but from my experience you cost will be nearly identical whether you use a 3'x3' or 4'x4'.

From NFPA #20 1999 Edition

A-4-2.2.2
The velocities in the approach channel or intake pipe should not exceed approximately 2 ft/sec (0.7 m/sec), and the velocity in the wet pit should not exceed approximately 1 ft/sec (0.3 m/sec). (See Figure A-4-2.2.2.)

Flow @ 2 ft/sec is 224 gpm and I've always gone with 4' wide x6' deep (at low water level) which handles a tad over 5,300 gpm. Good enough for a 2,000 gpm pump which is the largest I've done.

Of the 8 vertical turbines I've done in the past few years 6 have been for dry systems in cotton warehouses (2,250 gpm @ 150%) and I always use the same 4'x6' scheme.

Overkill perhaps but with nothing to be saved by going smaller why not?

Then, the case of a pond or open water source, there's the suction screen issue.

2-9.8* Suction Screening.
Where the water supply is obtained from an open source such as a pond or wet pit, the passage of materials that could clog the pump shall be obstructed. Double removable intake screens shall be provided at the suction intake. Below minimum water level these screens shall have an effective net area of openings of 1 in.2 (645 mm2) for each gpm (3.785 L/min) at 150 percent of rated pump capacity. Screens shall be so arranged that they can be cleaned or repaired without disturbing the suction pipe. A brass, copper, monel, stainless steel, or other equivalent corrosion-resistant metallic material wire screen of 1/2-in. (12.7-mm) mesh and No. 10 Brown & Sharpe (B. & S.) gauge wire shall be secured to a metal frame sliding vertically at the entrance to the intake. The overall area of this particular screen shall be 1.6 times the net screen opening area. (See screen details in Figure A-4-2.2.2.)

Using the B&S 1/2" mesh I need at least 25 sq. ft.. The channel has never been a problem, the size of the intake always comes down to required area of the screens.