Thread: 0t---salvage pumps

so i reviewed builder records of salvage pumps--aka trash pumps--and found an interesting factoid
pertaining to ability to handle solids
so a one inch discharge trash pump handles solids up to 0.5 inch
two inch discharge solids up to 1 inch
4 inch discharge ---2 inch solids
6 inch discharge==== 3 inch solids---and there is no advancement in solid diameter capability
in pump sizes larger than 6 inches

therefore--12 inch discharge pump has 3 inch solid handling capacity

i found no explanation in literature as to the three inch limit---but today--in process of
parting out a 10 inch barnes us navy pump--discovered the limiting geometry-- impeller
dimensions

the 10 inch pump was powered by 80 hp detroit 3-53 heat engine
flow volume an excepitional 3000 gpm--typical for 80 hp would be 1800 gpm
likely explanation is dedicated to naval ship pump out with low discharge pressure head requirement
therefore--increased discharge volume at tradeoff of lower discharge pressure

the critical measurement is height of impeller blisk--3 inches
blisk clearance from stationary pump frame is 0.010 in

therefore--no object larger than 3 inches in any dimension should be introduced into pump
cavity

my conjecture is probability of cavitation with suction feed limits pumps of this category
to 3 inch or less impeller blade height--comments welcome

I want to say most shipboard seawater pumps are 100 HP electric motor driven. Small ships have atleast four of them.

Dewatering a flooded/flooding space is not done with pumps, it's done with eductors. Every space with a bilge has built in eductors and many spaces have spare modular eductors ready for use. The eductors use firemain pressure to create a venturi and suck many times the water they use.

I don't know what the eductors were rated for, but I gaurantee it's way way more than 3000 GPM. Probably like 20k or 50K GPM depending on the firemain pressure.

I got to use the eductors frequently. I was firefighting teamleader on my ship and I was also in charge of the engine room. When we were at sea I would have the engine room guys powerwash all the nasty crap and train everyone in my division on how to align the eductors. They would empty a 10 foot deep bilge in an instant.

Had a 6" pipe break off at a seachest about 10 ft below the waterline. Not full flow, but there was a 1/2" gap or so. Lots of water. Eductor kept up with it just barely cracked open.

Lincoln electric published a series of books from the 1970's in which they awarded
companies that re-designed products using welding.

One job was dredging pumps, and they handle IIRC 12" rocks.
The article had very good pix of the impellers and housings as well.

In well pumps the eductor would be part of a system called a jet pump. I had no idea they would be used for dewatering, but an excellent solution for low head discharge.

The Eductor is the very same principle as a Penberty Injector used to recharge feedwater of a steam boiler... and the same principle used to draw detergent into a pressure washer. Works great, no moving parts, save for the stuff flowing through 'em!

eductor apparatus is new to me

this Dept of Navy film introduces sobering fact---12 inch square penetration in ships hull 15 ft below water line
introduces 14,000 gpm ----how to survive this event is one part of damage control lecture you dont want to snooze thru



"UNWATERING FLOODED COMPARTMENTS" 1950 U.S. NAVY DAMAGE CONTROL FILM 12984 - YouTube