Centrifugal pump restricted output

Click For Summary

Discussion Overview

The discussion revolves around the use of a 2-stage centrifugal pump for propulsion in a small boat, specifically addressing the implications of restricting the output nozzle size on flow velocity and pump performance. Participants explore various technical aspects, including pump specifications, potential cavitation, and efficiency concerns, while also considering the broader context of boat design and operational goals.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions the validity of the maximum flow rate of 100 m³/hr, suggesting it may not hold under all operational conditions.
  • Another participant emphasizes the need for a performance curve for the pump to understand its behavior under different conditions.
  • Concerns are raised about cavitation occurring when restricting flow, with one participant noting that efficiency may vary significantly across different flow rates.
  • Several participants express uncertainty about the intended application of the pump, with some assuming it is for propulsion while others suggest firefighting or bilge-pumping roles.
  • One participant confirms the maximum flow rate but notes it is likely only achievable under ideal conditions.
  • Discussions include calculations related to flow velocity and the relationship between horsepower and pressure, with participants attempting to compute necessary speeds for effective propulsion.
  • Another participant highlights the challenge of achieving practical boat speeds with centrifugal pumps, suggesting that a speed of around 15 mph is necessary for practicality.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the implications of restricting the nozzle size or the expected performance of the pump. Multiple competing views on the pump's application and efficiency remain, and the discussion is unresolved regarding the best approach to achieve the desired output.

Contextual Notes

Participants note that the discussion is limited by the lack of specific pump make and model details, which are necessary for more precise evaluations. There are also unresolved assumptions about the operational conditions and the definitions of performance metrics.

  • #31
I uploaded the data sheet... Let me know if you need anything I can provide.

Preparing figures on what it is going on...
 
Engineering news on Phys.org
  • #32
Weight 600lbs
8ft by 4 ft
Flat bottom with 2ft taper bow.
2" draft.

This a test platform boat.
 
  • #33
Dan Steill said:
Weight 600lbs
8ft by 4 ft
Flat bottom with 2ft taper bow.
2" draft.

Hull Area = 32 sqft
Displacement = 32/6 = 5.3 cu.ft.
Weight of Water = 62 lbs/cu.ft
Weight of Displaced Water = 62 x 5.3 = 329 lbs
Looks like your Draft will be around 3.6 inches.
 
  • #34
I was hoping for a proper technical data sheet . One with pump performance characteristics .

Without this information we don't know the relationship between pump delivery pressure and flow rate . We could make some guesses based on known performance of similar pumps but I'd rather have solid data to work with .

Go to the actual manufacturers site and see if there is anything useful there .
 
  • #35
Dan Steill said:
7.5hp. 100m³hr flow rate. 4 inch inlet. 4 inch outlet. ~50 psi

Pardon my units, but ...
100m³hr = 440 gpm
50 psi * 144/62 = 116 ft
water horsepower WHP = QH/3960 = 440 * 116 / 3960 = 13 BHP (assuming 100% eff.)
so you see, the listed 7.5 hp doesn't correlate to the flow & head. You really do need the pump curve from the manufacturer to begin. Plus as mentioned above, it will show you the head vs flow.
 
  • #36
The way I see it is that you can estimate performance based on this: I have used a 10 HP Johnson motor on the back of a small boat and to use something that is only 7.5 HP and guaranteed to be less efficient will probably get you down to a performance that would be similar to sticking a 3 to 4 HP outboard on the back. To stick a trash pump on a boat and expect much is foolhardy. Not to say that it would never move a boat, I am sure it would. We get results in several ways in this world. We go on prior established research of others in the form of specs and etc. which involves some math and other skills that we may or may not have, or we just try stuff.
 

Similar threads

How to select a pump for a venturi injector?
  • · Replies 8 ·
Replies
8
Views
4K
Calibrating Pump/Venturi (Air) in a Closed Recirculating Water System
  • · Replies 1 ·
Replies
1
Views
1K
Calculating the force from a pump + nozzle system
  • · Replies 6 ·
Replies
6
Views
3K
Positive displacement pump for spray nozzles
  • · Replies 7 ·
Replies
7
Views
2K
Determination of delivery pressure from pump
  • · Replies 5 ·
Replies
5
Views
2K
Centrifugal Pump: Water Pressure at 50m & 4 Bar Gauge
  • · Replies 4 ·
Replies
4
Views
2K
Maximum number of microchannels in parallel for a syringe pump
  • · Replies 2 ·
Replies
2
Views
1K
Help with water pump calculations
  • · Replies 1 ·
Replies
1
Views
2K
Selecting a Centrifugal Pump for High Pressure Circulation in a Closed System
  • · Replies 2 ·
Replies
2
Views
3K
Increasing water pressure without increasing pump output
  • · Replies 2 ·
Replies
2
Views
2K