Fix the pumps

Friday, March 09, 2007

Background on MWI pumps

I know I've been away for a while. Real life has reared its head, as it often does in post-Katrina New Orleans.

However, I've been keeping a very close eye on the Corps' work around town recently. In anticipation of some news about the floodgate pumps, I wanted to give readers (new and old) background information on the inner workings of those pumps.

The pumps are intended to remove rainwater from the city when the floodgates are dropped. The floodgates would be dropped to prevent storn surge from an approaching hurricane or tropical storm from entering New Orleans' three outfall drainage canals: 17th Street, Orleans Avenue, and London Avenue.

Currently, there are ten pumps at the Orleans Avenue canal floodgates, twelve at London Avenue, and eighteen pumps at 17th Street. All are the same size: 60" diameter. All are factory rated for about 200 cubic feet per second (cfs), though the actual capacity may be somewhat lower.

The pumps (60" Hydraflo HAC360 models) and their diesel drive units were manufactured by MWI Corporation of Deerfield Beach, Florida, under a Corps of Engineers contract issued January 27, 2006. The contract announcement is here, while the original specifications sent out for bid are here. MWI's sales literature for the Hydraflo can be found at this link.

The pumps are made up of two main components. The first is the pump assembly itself. Here's one of the Orleans Avenue pumps last October, after it and four others at Orleans Ave. had been pulled from the canal due to still-unexplained problems:

So you can see what's inside, here's some of the pumps on the ground at Orleans Avenue last spring before they were installed:

The above picture is looking into the discharge of the pumps, which is the top when they are installed. Here's a blowup with some of the major parts labeled:

The pumps are powered with hydraulic oil. The oil is supposed to be raised to 3000 pounds per square inch (psi) and then sent via pipe and hose to the hydraulic motor, which translates the energy of the hydraulic fluid to rotational energy on the shaft of the pump. The propeller blades attached to the shaft move the water upward through the pump and into large pipes, which discharge on the lake side of the floodgates.

The pump power units are far more complicated pieces of equipment than the pumps. They have large 735 horsepower, 1800 rpm Caterpillar diesel engines on them. The engines power the hydraulic power system through a gearbox, also known as a pump drive.

The heart of the hydraulic system is a pair of hydraulic pumps made by Denison Hydraulics. The pumps draw hydraulic fluid from a large reservoir on the power unit, raise the pressure of the fluid to 3000 psi, and send it to the pump. At the pump, the hydraulic motor spins the propeller shaft. After the hydraulic fluid passes through the motor, it goes through the coolers on the pump, and then returns to the reservoir on the power unit.

According to the Corps' Floodgates Operating Manual, here are the manufacturers and model numbers of these major components (where I've been able to, I've linked to the literature for the particular model):

Drive unit engine - Mfr: Caterpillar model: model 3412
Pump drive - Mfr: Durst model: 2PD10
Hydraulic pump - Mfr: Denison model: T7ED
Hydraulic motor - Mfr: Rineer model: 125 four-port (not enough info in manual to figure out exact model)

What can we do with this information?

I ran some numbers. If the Caterpillar engine is rated for 735 hp at 1800 rpm, that converts to a rated output torque of about 2144 foot-pounds. Then I looked at the rating sheet for the Durst pump drives.

According to that sheet, one is supposed to take the rated torque of the input to the pump drive, multiply it by a service factor, and then compare that number to the maximum rated torque of the chosen Durst Model (a 2PD10, in this case).

In our case, the service factor would probably be 1.5, which corresponds to a multiple cylinder internal combustion engine with uniform (i.e. no shock) loading. So we multiply 1.5 times 2144, giving 3216 ft-lbs as the number which the Durst drive's rating must beat.

According the rating sheet, the Durst 2PD10 is only rated for 1996 ft-lbs, which is less than the nominal torque from the engine, let alone the torque modified by the Durst service factor. The 2PD10 is the biggest two-pad pump drive in the Durst product line. It would appear that the Durst pump drives on the MWI drive units were severely undersized.


  • From Compuserve political debate forum
    thread title "Pumps in New Orleans"
    msg # 34

    <...It's Mere's casual nonchalance concerning the use of non-factual facts,and boasting of questionable spousal expertise>>

    After skimming through the US Army Corps of Engineers' specifications and the MWI pump catalog I have extracted some technical facts which I posted in msg. 32. You must read the whole message because the partial one contains insertions by the forum software
    I don't expect either you or Merelynn to understand the details but basically this is what I said
    1) Someone? had already selected the MWI model HAC 360 pump and wrote the specifications around it, probably with the assistance of a vendor of that company. I refrain from guessing whether or not there was political influence
    2) That someone?also dropped the capacity requirements from the catalog value of 134,000 gpm to around 100,000 gpm, a reduction of 25 percent... why???
    3) The horsepower figures are also way off base, one too high by 100 percent, It would be like you buying a car with an advertised mileage of say 30 miles per gallon and when you drive it, you only obtain 15 , so the gasoline (energy to operate) costs you double of what you expected to pay.
    4) Some requirements in the specs obviously were bypassed, such as, the pumps shall all be shop tested with tests witnessed and certified by some professional engineer. If this requirement had been followed, obviously they would not have been defective in the field

    By Anonymous Anonymous, at July 01, 2007 8:32 PM  

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