Water brake dyno coupling

[rlo943]

Just looking for some advie on an engine dyno I am trying to make. looking into alternative load devices, Water brake AC motor/invertor. Can anybody offer any advice on sourcing a water brake capable of around 170 HP ? Also can anybody offer some advice on the use of a fluid coupling converted to a water brake ? Any how to control the torque on such an item? Thanks in anticipation of some advice.

 

[MikeHalloran]

The water brake _is_ a fluid coupling, with its output shaft fixed. The torque is regulated by controlling the amount of water that's resident in it.

It's not as simple is just filling it with a controlled charge of water and sealing it up, because the water gets very hot very fast... so you have to circulate and cool it.



Mike Halloran
Pembroke Pines, FL, USA

 

[Bribyk]

There are a lot of dynamometer manufacturer's that have water-brake models in the 170 bhp range. You will need a cold water supply with 30-60 psig flowing 8-9 gallons per minute (approx 1 GPM per 20 hp), depending on the manufacturer and design. You can run the water inlet valve manually or setup an actuator and PID loop to automate it.

You may also want to look into an eddy-current style absorber, but they (usually) still require water to cool them.

 

[rlo943]

Sorry should have made myself a bit clearer. What I am looking at is a fluid coupling which would normally be placed between a motor and a gearbox to reduce the strain on a gearbox during motor DOL startup.these are normally filled with oil and sealed with a solder cap which will blow if the temperature become too high. Like the items in this link.

http://www.flender.com/content_manager/page.php?ID=412881&dbc=8bea2ed1b93096332a3805c4cf73467f.

The plan was to install this device with a trunnion bearing on both sides. Connect one side to the engine and the other mounted onto a loadcell to read the torque. I plan to remove the filling and draining point and use this to pass water through it. But what is the best way to control the water level? I have experience with various needle valves and linear valves/controllers. But should this controll the flow to the unit or the temperature at exit or the exit pressure?? Hope somebody can help. Thanks

 

[MikeHalloran]

What has to be controlled is the amount of fluid that remains in the coupling, while simultaneousl adding cool water and removing hot water. You may have to modify the coupling internally to do it.



Mike Halloran
Pembroke Pines, FL, USA

 

[rlo943]

Its surely quite hard to control the amount of liquid that is in the coupling when it is rotating ? Any idea how they do it in a proper water brake dyno?

 

[Bribyk]

A dyno typically works like a pump (or mechanically like a generator). The housing (stator) side doesn't rotate, it sits on bearings on the dyno shaft (which the engine or motor drives) and it attached to the load cell to measure torque and keep it from rotating around the shaft. The shaft is fixed to the impeller (rotor) which spin as an assembly inside the housing. The water enters near the top of the housing and exits the bottom. Hope this is clear.

 

[rlo943]

Your description is exactly what I am in the process of making at the moment, But how can you control the level of water within the brake/pump? By controlling the water flow on the output side/bottom of the pump? or controlling the pressure in? or controlling the flow in?. If the water flow was not regulated in any way I presume the water level in the brake would not be constant therfore not stable enough for power monitoring/ trending, But sounds like we are in the right track.

Thanks in anticipation of your help>

 

[patprimmer]

The ones I use have a knob on the consol that controls a tap. I don't know if it's the inlet or outlet pipe, but I suspect the outlet as with constant inlet, the head height would be set by the outlet. This seems more reliable and accurate than the other way round.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Warpspeed]

I have no idea where you are rlo943, but there is a suitably small complete water brake engine dyno advertised right now on e-bay in Australia at a very reasonable price, that might be of some interest to you.

I hope I am not transgressing any Forum rules mentioning this, so will not give a direct link to e-bay.

Another resource is the Flow Bench and Dyno forum. There is a long thread there in the "dyno" section with a lot of pictures and technical info about home built water brakes.

http://www.tractorsport.com/cgi-bin...1499a96c3ed45a17d435a72df619a8;act=ST;f=4;t=7

 

[Bribyk]

Most basic dynos use a throttling valve on the water inlet while the outlet has an appropriately sized orifice to control the drain rate.

The amount of water in the dyno determines the torque resistance and the flowrate through the dyno is determined by the power (need to absorb XXX power so need YYY amount of water flowing through at a temperature difference of ZZZ). The water outlet temperature needs to be low enough to prevent the water in the dyno from flashing to vapour (some cavitation likely occurs though).

More advanced dynos use control valves on both the water inlet and outlet which I assume allows for a greater torque/power range to be accommodated.

 

[Bribyk]

My previous post was slightly incorrect.

Both the water level and the speed of the dyno determine how much torque resistance there is (you get more torque at a higher speed for a given water level). Once the dyno is full at a given speed you have maxed out its torque capacity. If you increase the engine speed you will then have to increase the flow rate through the dyno, while keeping it full, to keep the water temperature acceptable.

 

[waross]

Putting water in an oil filled fluid coupling may shorten the useful life. If you drill out the fill plug, you may need to also drill a drain hole.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[patprimmer]

Bill

We are talking about a water brake which is a water filled coupling with variable water level to control load. It is designed from day one to run in water.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[waross]

I know Pat, but this comment in the original post worries me!

Also can anybody offer some advice on the use of a fluid coupling converted to a water brake

and again

these are normally filled with oil and sealed with a solder cap ..........I plan to remove the filling and draining point and use this to pass water through it.

Respectfully

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[patprimmer]

Sorry Bill

I should have reread the OP before commenting.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[rlo943]

Can you elaborate on the "this worries me" please After discussions with the manufacturers these items I am looking at can also be run with water for mining applications, And that is the reason I am posting a question here to try and find out why this cannot be used and what the fundemental differences are?
Thanks

 

[Warpspeed]

Many things designed to run with oil are constructed from cast iron or mild steel, and work fine.

Anything made out of cast iron or mild steel will corrode at unbelievable speed with HOT water. Especially hot water that has any dissolved oxygen in it.

The hot water pipes in your home will only use copper or brass fittings. The cold water pipes may be iron if the house is old.

A water brake made from fairly thin pressed mild steel parts will not last very long. With oil, corrosion is a non issue.

 

[patprimmer]

As well as hot water, you might have cavitation hot water at some points. This will further significantly aggravate the corrosion problem if the brake is not constructed to take that use.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[rlo943]

I appreciate your concerns, But the unit I am discussing is made from an aluminum casing and I will deal with any corrosion or wear problems in time. But basically what I am asking if anybody can explain the fundemental differnces between the two items if any??