Magnetic Drive & Seal-less water pumps

[hydromech]

Hello...

Has anyone got any ideas of, or has anyone seen a water pump with a magnetic varible drive coupling.

One without a shaft seal would be nice.

We have considered many ideas but we really need some inspiration.

We need a strategy that is fail safe, with a mechanism that seperates the magnetic drive plates and reduces the speed of the impeller to reduce flow.

Fail safe means maximum flow on start up.

Ideally, the pump control will respond to temperature and or flow and or pressure...

Mechanical only, no electronics allowed, for commercial reasons.

Seperating force of drive is in the region of 300-400N.

Any ideas..?

Adrian

 

[pumpking]

Not sure such a beast exists !! Magnetic drive couplings cannot slip to provide pump control, the most common coupling is a synchronous drive, and if there is the slightest bit of slippage, the Impeller simply stops until the magnets re-synchronise.

It sounds as though an inverter can be your best solution, and many applications we deal with are Inverter driven to control systems.

http://www.cdrpumps.co.uk

details some pumps suitable for this drive method.

Inverter drive, or even the Lowara Hydrovar is used frequestly to control processes on many kinds of centrifs, and they are now pretty cheap compared to a few years ago !!

 

[Valvecrazy]

The only magnet drive couplings like you are talking about that I know of, go between the pump and motor. Therefore they still require a mechanical seal. They also require electronics (4-20 ma signal) to vary the impeller speed according to the flow or pressure required. If you are only pumping fairly cool water, you should consider a Constant Pressure Valve. They are pressure operated, have no electronics, and can vary the flow to maintain a constant pressure. The power required by most pumps will drop off by simply restricting the flow from the pump with a valve, the same as it will by slowing the RPM with a drive. This makes for a very simple and dependable pump control with out any electronics. They also have a built in minimum flow to keep the pump and mechanical seal plenty cool.

 

[Strong]

Adrian,

What is motor speed, horsepower; pump pressure and flow; static pressure and temperature at the magnetic drive boundry? When you say "mechanical only" for the speed control, do you mean a manual control mechanisn with movement by operator. If not, then would you consider a electro-mechanical device for speed control?

Walt
w_f_strong [at] msn [dot] com

 

[hydromech]

Thanks for the replys

The application would be on a commercial diesel engine.

We have a basic concept in that the normal mode of operation for the magnets would see them close together giving full drive speed from the engine.

A wax cell or similar would be used to seperate the magnets causing the drive to slip and the pump to run slower, reducing parasitic losses in the engine.

The problems we have have are maintaining fail safe operation...keeping full flow when the engine starts but then increasing slippage quickly when the water is cold or reducing slippage if the water becomes hot. Pumping lots of cold water around a cold engine wastes fuel. Pumping no water around hot engines is not good either.

Also the seperating forces of the magnets are in the region of 300N and the energy losses during slippage are huge.

Not to mention the magnets attracting all of the loose ferrous particles in the coolant.

For information...one of the magnets would be on the drive pulley and the other on the impeller. No drive shaft between means no shaft seal.

It is as we suspected...over ambitious!

Thanks again...

Adrian