home made water brake

[Tony]

The only water brake I have ever seen inside, (which was not a Land and Sea unit), had straight radial vanes inside the casing end plates that had similar dimensions to the straight radial vanes on either side of the rotor. The only difference being the number of vanes.

If both rotor and casing had the same number of vanes, all the vanes edges would pass each other simultaneously, potentially causing a massive torsional vibration problem. It would probably shake itself to pieces very quickly. So the outer casing end plates will have either an additional vane, or one less vane than the rotor. That will then create a far smoother more constant torque load.

The water flow control valve interests me too. I am assuming this is a normal commercial motorised gate valve of some description ?

The recommended water flow sounds about right, I used British imperial gallons and degrees Celsius in my previous post. Flow measured in US gallons and Fahrenheit will cool the dyno just as well, hehehe.

[DaveMcLain]

When I originally set up the dyno the load valve was the manual load valve and it's really just a simple water valve with a high flow capacity. The servo load valve is electrically opperated and the motor rotates a slotted cylinder that gradually opens more area to the inlet the farther it rotates, this allows the stepper motor to control the valve very quickly in small steps. You can still use this valve for manual control too by rotating the knob on the top. The valve opens and shuts much more quickly than the manual version so you don't have to move the knob very much to control the engine.

I never counted the number of vanes in the housing but it would make sense for it to have an uneven number when compared to the rotor. The rotor does have a ring of holes about 5/8 diameter right near the root of where the vanes attach at the center hub, one hole for each vane right near the tip of the pie so to speak. No coincidentally this series of holes lines up closely to the water inlet port on the back of the water brake housing.

Also, I was looking in the back of my Land and Sea manual where they have a load chart for a full absorber. The 13 inch single rotor absorber's torque capacity is about 925lbs/ft at 3000rpm, it's torque capacity declines from there at a very gradual rate to 600lbs/ft at 10,000rpm. The slope of the curve going up from 1000rpm to 2000rpm is very steep going from 200lbs/ft at 1000 to about 780lbs/ft at 2000rpm! Again, these figures assume a full absorber, my setup seems able to approach these maximums within 100lbs/ft or so from my experience at 5000rpm, I've had around 770lbs/ft at 5000rpm and held that load, on the chart it shows that it can go as high as about 860lbs/ft at that rpm.

The smaller absorbers, the 7 and 9 inch versions have much less torque capacity and they peak at a much higher rpm than the 13 inch, great for testing smaller engines.

[Sandra]

Is there anyone who has any pictures of the insida of a waterbrake? Both the impeller and the case.. Have searched for a long time but never found anything. Help me...

[Tony]

Dave, thanks once again. The ring of holes in the rotor sounds logical for balancing the air/water on both sides of the rotor. The water brake I looked at many years ago, had a water entry and a vent on both sides of the casing, but I don't remember seeing any rotor holes.

Sandra, The link to the Rochester Institute of Technology small dyno project, given earlier in this thread has several very clear pictures of the rotor design.



The inside of the casing in their design was just a smooth drum. But for much higher torque capacity, the outer casing should have straight vanes as well. The inside of a vaned casing appears exactly like looking at one side of the rotor. The vanes are an identical size and in an identical position. The centre bearing boss even looks almost the same. The only difference is having one more or less vane than the rotor.

[Sandra]

Ok, now I know a little more about it. What is the distance between the impeller and the case? If anyone have more pictures of case or impeller it would be welcome.

[DaveMcLain]

The top of the rotor vanes come very close to the fins in the case, I would say within about .010 or so. Some years ago I had a bearing go bad in my absorber and it messed up the rotor because the fins clashed with the case. It wasn't anything too serious, it started making noise audibly and also in the torque data, I changed the rotor and put in some fresh bearings and it's been fine. For what it's worth, the old rotor did not have the holes near the center. Is the performance of the brake much different? Not much really it seems to work about the same but it's been a couple of years since the over haul.

[RRBD]

On my Stuska, it has .125" clearance on diameter and side to side. there are 15 pie segments on the Rotor and 16 segments in the case sides. The Rotor is 2" thick.
I am going to build a Absorber with a 12" Rotor, it will have .050" clearance eveywhere to start out with.
Scott

[gofaster]

Here is a link for a nice dyno schematic:

[DaveMcLain]

I'm not so sure the clearances really matter all that much because you are after all turning about 2 inches worth of fins through an absorber filled with water that's also churning against 2 inches of fins in the housing. Believe me, it can make itself tough to turn in a hurry.

[gofaster]

I found a link that explains how a strain gage works.



The gages I've seen before looked like a plain piece of steel. The resistance grid was not visible, and this topic really piqued my curiosity about them.

[86rocco]

Stuska dynos, the older ones at least, have a hydraulic load cell rather than a strain gauge. You can think of it as a master cylinder connected to the torque arm with a pressure gauge to display the torque. Right now, I'm working on putting together a crude data aquisition set-up for a friend's old Stuska. My set-up will consist of a piezo-electric pressure sensor t'ed off of the existing pressure gauge to measure the torque, an optical rpm pick-up on the ring gear of the dyno, an in-expensive commercially available computer interface and the software that can with the interface. I've bench tested everything, so far, everything looks great. I'll post up some screen shots when it's up and running.

[bruce]

I have a couple of strain gages to sell if anyone would like one? Think they are good for 0-500lbs-ft, I'll take a look when I'm in the shop tomorrow.

I'm also working on a DAQ setup for my dyno using the Dataq DI-194 card. It is limited on it's speed but if I can get it to work I can always upgrade to a faster DAQ card later. I have absolutely no experience when it comes to DAQ so it has been/is a learning experience for me.

I sure can't afford a commercial based unit at this time, would like to make contact with anyone else who is working on something . . . 86rocco?

[86rocco]

The trickiest part of cobbling together a system with inexpensive general purpose a/d units like the DI-194 is getting a good rpm signal. I'm using the sensor interface. I chose that unit because it's relatively inexpensive, it has built-in RPM pre-processing and the Logworks software that comes with it is fairly powerful with a nice, easy to configure user interface. Plus, the system and software are expandable allowing me to add various goodies like wideband O2 and egt as my needs require or my budget allows.

[Dave W]

when you guys do a pull and the torque arm pushes or pulls on the strain guage is it equal to the amout being applied or does the guage have to be calibrated to the water brake.
Example:
500 foot pound of torque at 5000 rpm with a one foot torque arm. If I were to place a scale under the torque would the scale say 500 lbs at 5000 rpm.

Another question for Dave M.
The hose to let the air out of the brake is it mounted on top of the unit and does the outer part of the brake which would be the stator or housing rotate freely around the shaft.
Thanks Dave W

[gofaster]

I found a webcast that I felt did a nice job explaining how to use the PC for data logging. This site required me to register, but it didn't cost me anything. Their home page has various menus regarding strain gages, temperature, etc. and how their system works with a PC. It may be an over simplification for many forum members, but it clarified things for me.



Request to view:

"Build a Data Logging Application Out of a PC with a Basic Understanding of Windows"

At two points in the presentation he pauses to ask questions on an interactive screen. The screens are inactive, and you'll need to wait a minute or so for the presentation to continue. The first time I watched it, I thought my computer locked up! The second time through, I waited and sure enough the show continued.

It made me realize that making physical tests and keeping a realtime and replayable record and analysis of it may not be as difficult as I previously thought it would be. I think a DIY'er could make good use of the information.