Offshore water pump. 6

[jamesss]

The project;

I am currently working on a pumping system to draw/pump water from the sea, to the access level of offshore wind turbines.The sea water will be used to wash off bird waste that accumulates in large quantities causing problems for offshore operations.
The pump will be a self priming centrifugal pump 230 v 160L/min 5 Bar.
The suction line is 7 meters maximum length, 1.5 inches diameter pipe.The discharge line is also 7 meters but has a diameter of 1 inch.The pipe diameters are matched to the inlets and outlets of the pump design.
There is a non return valve on the suction side 3 meters from the pump, this is to maintain water in the pump body and discharge line to assist with priming.
There will be a control circuit activating the pump at high tides only and during night time i.e. one high tide per day.

Testing of the self priming pump, suction hose,non return inline valve offshore.

During high tide the pump was situated on the resting platform (7 meters from sea level to pump inlet).the pump body was then filled with water ready for self priming.The suction hose was placed into the sea water and the discharge hose was run uptothe turbine access level 7 meters up.

When the pump was activated, i could see that the pump was extracting air from the suction hose through the pump housing and into the discharge hose, the air bubbles and water mixture would rise so far and then fall back into the pump housing. After 5 minutes i turned the pump off and could see the trapped air in the pump housing beginning to naturally rise up through the discharge pipe and out into the open.When reactivating the pump after all the air had vacated the pump casing, the pump performed as it should,displacing water from sea level upto the turbine access level at a rate of 80 liters per minute.

Each time i turned the pump off and then back on, it would activate and start pumping straight away however, when i turned the pump off and introduced air into the suction pipe to simulate the tide going in and out, the pump would not prime and would continue to collect a water/air mixture in the pump casing and fail to prime fully, leading to failure to pump.As mentioned, if i turned the pump off then on to allow the air to escape the casing then the pump would perform faultlessly.

After investigating further into the reason the pump was failing to prime first time, i came to the conclusion that the head of water on the discharge line was not allowing the air/water mixture to escape resulting in air binding thus loosing suction.

My questions,

Is this something anyone has seen before?
Is my conclusion plausable?
if so, would an automatic air breather installed on the pump casing be of use for my problem?

I don't really want to re-configure the control circuit so the pump activates twice as i don't see that as a sound solution to the problem at hand.

Any help will be much appreciated!

 

[Artisi]

Seems like it might be time to employ a pump engineer to sort out the mess, think yourself lucky it's only a toy pump and not a few hundred kW's.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[jamesss]

Artisi,
Mess?

Nothing is installed?
That’s the whole point of test stages?

Leave you to your manly big pumps.

 

[TugboatEng]

The mess part is all of the equipment you bought that clearly doesn't work. Since you've bought it you're going to try to make it work regardless of feasibility. Sometimes the right answer is to bin it and start over, maybe bring in an expert who can steer the project.

 

[jamesss]

Tugboat,

All this equipment?
A pump?
What are you going on about?

I’m in the process of sourcing a submersible pump suitable for the job??

There has been some good knowledge and experience shared on this forum, don’t post if you have nothing constructive.

 

[TugboatEng]

You have bought a pump and installed it on a test rig. You were trying to make the pump work despite it being the wrong one for the application. That pump would cost $3000-4000 USD if it's a bronze casing. That's no trivial expense to eat. If you used the appropriate corrosion resistant piping that will not be inexpensive, either. I wasn't trying to be negative. I thought this was a good chance for a lesson. Self-priming pumps aren't reliable for unmanned processes.

I guess I spent the day trying to figure out how to make a toilet flush better so I had to pass the frustration on to the next guy.

 

[jamesss]

Tugboat,
There is no test rig and and the pump was a fraction of what you estimate.The piping can be used again?When cleaning the assets cost hundreds of thousands to clean manually each year then it is small change.The pump will not go to waste neither will the knowledge gained on this board.

Before you post worthless non-constructive posts, find out all the facts matey.

Thanks again to all who posted and assisted me with this project, especially littleinch, very informative indeed.

 

[Artisi]

Such a pump requirement is a simple straight forward pump installation and would take any guy with a basic understanding 20 minutes to select and come up with a viable solution.
You say it's for an asset worth hundreds of thousand - so spend a couple of hundred dollars and employ someone to sort it out.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[jamesss]

Artisi,
Okay may friend, if you say so

 

[Artisi]

Yes, I do say so.
Let's look at your very first post and investigate why / where the "air" comes from in the suction hose when the tide goes in and out.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[jamesss]

Artisi,
There is one of you on every board.

The project has moved on...so should you