home made water brake

[DaveMcLain]

The absorber is amazingly small for the amount of power it can handle, it has low inertia too and I think that's important when testing lower horsepower stuff. When I built the dyno my intentions were to run engines under about 500 horsepower most of the time this would include most all small blocks. As it turns out, I've run engines that are all over the map horsepower wise from my 120 horsepower flathead to a 900 horsepower 557 Ford.

The rotor in my Land and Sea absorber is aluminum 12 inches in diameter with 12 fins per side that stick up about 3/4 inch on each side. The most powerful engine I've ever had on there made 906 horsepower at 6900rpm and 763lbs/ft torque at 5300rpm. This was ALL my absorber wanted to handle even with 75lbs water pressure through a 1 inch hose I could not sweep slower than 600rpm/sec during the power pulls. To be fair, this absorber is VERY effective and rated to 800 horsepower with a water supply like mine, it'll do that very easily. Mine is the single rotor design, they also have a dual rotor absorber that's rated to 1600horsepower, same diameter, just twice as thick!

[DaveMcLain]

I dug around and I found a few more pictures of my dyno from back when I first got it together.


Water brake from the rear see how the drain comes out of the bottom at an angle. RPM pickup goes in just under the rear bearing, see the grease fitting and some grease weeping from the seal(normal, it should do this so that moisture is forced from the bearing when greasing). Notice how absorber sits behind the adapter where the bell housing attaches and the adapter just sits on the top of a piece of 1 inch all thread that's been turned down to fit into a plastic bushing. This makes it easy to line up when switching engines.


Very simple and effective motor mounts made from a piece of steel, a length of 1 inch all thread and 2 one inch nuts. These mounts were easy to build and work great. In this picture I'm using a circle track mount on a small block Chevy. Sometimes depending on the headers, I'll grab the front of the engine with an L shaped bracket instead. Remember, the mounts only have to hold up the engine they do not transfer any torque what so ever. It's nice to be able to easily adjust them depending on the engine. The flat pieces of metal bolt to the stand through slots that I milled into the tubes(5/16 wall 2x2 box) inside a nut is welded to a piece of strap so it can't turn when the bolt is tightened.



Water well pressure tank. This was before I was supercharging the tank with a pump and with about 45psi from the hydrant here in the shop the absorber could easily hold back 500 horsepower or a little more, probably close to 600. Later when I needed more capacity, I put on the pump and pressure switch and check valve and bumped the pressure up to 75psi. High volume is what you need generally, not high pressure that's why having the tank alone just to act like an accumulator works great, cheap too, I found it for free at a local scrap yard!

[bruce]

Is anyone else seeing this thread/posts all "messed up"? The posts are not following in sequence in the actual thread?

I'm not sure what is happening, think we need to start a new thread on this subject.

[86rocco]

Yes, sometimes I don't see the most recent post or two but if I click on "Post Reply", they appear.

[DaveMcLain]

Is it really messed up? I just posted these pictures of my water tank and absorber today and it seemed to work fine. A few days ago when I posted some pictures in this thread it seemed to take a while and acted like the thread was locked, I wonder if the server was just down for service or something?

[bruce]

Actually the other day I had closed this topic (sorry I forgot to open it till later in the evening when I remembered) trying to figureout why it seems messed up. It appears that two topics got merged into one thread.

[Tony]

I am still having some difficulty getting my head around exactly how these water brakes work. This is my simple understanding so far, Dave please correct me if I have this all completely wrong.

The rotor spins around in a drum type outer casing, and the water will distribute evenly around the outside periphery from centrifugal force, rather like a washing machine on spin dry cycle.

The depth of this rotating water layer can be controlled by suitably adjusting the relative water inlet and outlet flow during operation.

Sufficient water flow is only required to carry away the heat, the actual braking force comes from the depth of the distributed internal water layer around the inside periphery of the drum.

The rotor has twelve vanes, and each side of the drum also has internal vanes in close proximity, presumably eleven or thirteen ? The actual braking force is generated by shearing forces in the water, as the moving vanes pass very close to the stationary vanes.

Braking force can be increased or decreased by adjusting the water depth around the inside the drum. The water exhaust port is fixed in area, and the water feed volume can be adjusted to hold the desired load.

The Rochester Institute of Technology was a simplified design that used no internal vanes in their drum. Presumably because it was a very low power low torque dyno. For much higher torque capacity in a small size, especially at lower Rpm, the stationary drum will definitely need some fixed internal vanes, yes ?

After some thought, I am assuming one rather clever hidden feature of this design. As Rpm rises the braking forces would also tend to climb at a very high rate if the water level in the drum was kept constant. But this particular design would also tend to try to pump itself dry as speed increases. That is because the water inlet volume is fixed, but the water exit volume increases with Rpm, as centrifugal force and internal water pressure increases. So as Rpm rises, the water level in the drum actually falls to keep the torque absorbtion rate fairly constant with Rpm. This is all a guess on my part. Thoughts on this anyone ?

[DaveMcLain]

I think you are absolutely correct in your thoughts of how the water brake power absorber works. In my situation I have plenty of water volume so I run with the largest outlet on my water brake. This makes it more responsive when reducing the load(clears out the water more quickly for a given amount of rpm). Don't forget also that there is a small vent hose that's also attached to the water brake, it attaches near the center just like the feed hose. This allows the brake to empty by pulling in air as water is forced out by the rpm.

The waterbrake dyno tends to become a better power absorber as rpm increases. My dyno will easily hold an engine making 500lbs/ft at 2800rpm but it takes a lot of water to do that, as rpm climbs, it actually gets easier, the torque capacity increases, rather quickly. In fact, I bet it takes less water to hold 600lbs/ft at 5000rpm than 500lbs/ft at 2500, without question. Very low rpm high torque engines are the most difficult loads for the water brake to handle. High rpm high horsepower is generally no problem as long as there is enough water volume passing through the brake to carry away the heat.

A long time ago when I first had the dyno up and running we were trying it out with a customer's engine. It made around 300 horsepower at 5300rpm. Running of the hydrant and garden hose alone was not quite enough water volume. To allow me to load the engine I put a restrictor in the outlet of the brake to reduce the size from about .375 to around .187. This allowed the brake to fill more completely with less water since it was blowing less out of the drain. This worked but it made the outlet water incredibly hot, too hot.. Steaming hot. Land and Sea does not recommend getting the absorber too hot and recommends a max outlet temp of about 180 degrees. Now with my water supply it comes out only lukewarm.

[jsa]

[Tony]

That is most encouraging Dave.

Yes, the vent hose will be a very important feature to prevent water flow from being influenced by trapped internal air pressure variations.

I have just been doing some water flow calculations here. To dissipate a continuous 500Hp would require 20 (imperial) gallons of water per minute, and that would raise the water temperature by around 59C. That is "fire hose" territory! So I can certainly see the need for a rather large volume of stored water. A fully closed loop cooling system just may not be practical without using an extremely large evaporative cooling tower.

At that sort of flow, one inch supply pipe to the dyno may be a bit on the small side. Something a bit larger would be able to handle the flow with less supply pressure.

But the exit pipe can be a fair bit smaller because the pressure build up off the rotor will really force the water out under extremely high pressure, so that will be less of a worry. If it creates a seventy five foot high fountain, that is a LOT of pressure.

[DaveMcLain]

Here's what Land and Sea says about the water supply requirements: Assuming a 50 degree inlet temp the minimum water flow through the absorber should be about 1 gallon per minute for every 20 horsepower(to keep the water discharge temp below 180 degrees F) More powerful engines require larger diameter supply hoses, higher volume pumps, increased delivery pressures and larger absorber drain orifices.

For testing at 200horsepower you will need at least 10GPM(US Gallons) at approx. 18+psi
For 400 horsepower you will need at least 20GPM delivered at about 30+psi
And for 800 horsepower you will need at least 40GPM at 40+psi.

What's interesting is how they rate the psi, dynamic. What you do is have a pressure gauge screwed into the port on the side of the load valve. Unhook the -16 line from the absorber and with your water supply hooked up and load valve closed look at the pressure. Then you open the load valve all the way and see what the pressure goes to, that's the pressure they are talking about when they say 40gallons per minute at 40psi, a lot of water! That's why I use the pressure tank, it produces a stable pressure and a very high volume for a surprisingly long time, plenty for any pulls I've ever done even at high horsepower. Think about it, a pull from 3000rpm to 7000 at 300rpm/sec is only going to last about 15 sec total from the time you open the load valve till the end of the run. It only takes a second or two to get the engine loaded at the start rpm/hold point.

Here's some more info from the Land and Sea website, good stuff:

[Dave W]

Dave what was the major cost in building the dyno? Software, Brake, Strain gauge. Do you have this thing hook to a laptop?
How do you operate the dyno from the start? Water on first, release the clutch and giver ####. You really got me wanting one now, great pics keep us informed.

[DaveMcLain]

I'm trying to remember what everything cost but I think the cost of the absorber and torque arm was probably the biggest thing. I bought the DynoMax software package, brake, manual load valve and computer all at one time.

The little DynoMite computer can run completely self contained and for the first few days I ran it that way. With the manual load valve you run the pulls differently than with the automatic setup that I have now.

The little computer on the test stand connects to a PC that I built myself through a comm port, I use about a 20ft cable. Having a large monitor is also a great addition, it doesn't take much computer power to run the DynoMax software and the newer version that I'm using now, DynoMax 2000 is very good with many more features, better graphing and a lot more capabilities than the old stuff.

The way my setup works: I have the little computer turned on and communicating with the PC, it reads out data in real time on the screen, EGT's, RPM, Torque, Horsepower, Engine Temp, lots of information.

I go into a tab on the PC software where I program my automated test, I tell the computer my start/hold rpm, end rpm and sweep rate. Then with the real time dyno screen open I start a new run. Over on the dyno test stand the servo load valve which is controlled by the computer is powered by 12 volts, I leave this turned off for manual operation, it's easier than switching it through software but this is also possible. I switch that on, double check my water pressure to see that it's at about 70psi. Then I open the throttle on the engine smoothly and not too quickly so that the computer can catch and load it to the start rpm. This takes about a second or so and then when the engine rpm is stable I press R on the keyboard. Using a wireless keyboard is a great feature but a long cord is also ok. I set the keyboard next to me on top of a tall stool when I'm running a pull.

The engine then starts it's run leaving the preset hold/start rpm and sweeping toward the stop rpm at whatever rate I told the computer to use, 300rpm/sec is what I use most of the time. But you can use nearly any rate you want including step tests where you hold at various rpm throughout the pull(produces higher numbers because the engine has no inertial losses).

When the engine reaches the stop rpm the computer increases the load so that it's rpm stops climbing, I then just let off of the throttle smoothly, switch off the servo, let the engine idle for a little bit and then turn off the ignition.

If you check out the dyno pull video you can see me start the test, I have the engine running first, you can see me switch on the servo, load the engine and then hit the key to start the pull. At the end, I switch off the servo and shut off the engine.

Now that the data has been captured into the computer it can be analyzed by graphing and looking at the numbers. At the end of the pull I enter my weather data that's used for correction purposes.

Things that are automatic are the cooling tower, it's thermostatic valve lets in fresh cool water to keep the engine temp constant. It's non pressurized and the tank has a standpipe so the excess water just spills over and goes out the yellow drain hose. Generally I let the little CSI pump run most of the time to keep coolant circulating after a pull, at least for a minute or so, if we're going to be down making changes for a while I switch it off.

My dyno has a regular car battery mounted on the stand and most of the time I also hook up a battery charger while testing to keep the voltage up. Also, the dyno is equipped with an MSD 6AL ignition box, coil, adjustable timing control and start retard. I have an rpm switch so that I can select an safe rev limit for the engine I'm testing, most of the time that'll be 4 or 500rpm above the stop rpm, just in case something would brake, no harm would come to the engine.

My fuel system on the dyno is the result of years of working and coming up with new ideas, having an electric fuel pump is just about mandatory, you can do it without one but it's sure nice when you're messing with jetting. My fuel pump is controlled with a toggle switch, momentary switch AND an oil pressure switch. With the toggle on, the pump will run whenever there is oil pressure. With the switch on you can energize the pump with the momentary switch(fill the bowls, check for leaks etc) without the engine running. Switch off the toggle and run the carburetor out of gas if needed, works great. A bypass style regulator, mine is a BLP modified Holley piece is also an asset. This regulator has a small jet so it always returns some fuel to the tank. This allows you to push the air out of the system quickly at the start of a day's testing. Fuel pressure is adjusted at the regulator which is mounted at the end of the fuel rail. Pumps never "dead head" against a regulator and only pump the pressure needed so they don't work very hard. For pumps I'm using two Holley Black pumps fed by and feeding a 5/8 fuel hose, return is a 3/8 hose. The filter is one from a Detroit Diesel engine, a canister with an any fuel element that costs about $5 if it needs to be replaced, will filter gasoline or methanol.

Extra heavy battery cables and a Ford solinoid pretty much round out the equipment. I have a full set of gauges, 8000rpm analog tach, oil pressure gauge (with extra large line for quick response), temp, fuel pressure and manifold vacuum.

Any more questions? Ask away... I had about a million questions 7 years ago when I was planning this venture. My dyno is nothing to look at really and the reason for that is because it's always in a state of flux. It seems like I'm always coming up with some new way to do things but now at least most of the support systems are very well worked out.

[Tony]

A few further thoughts on this.

These dynos seem to be made completely from aluminium, and no mention is made about hard anodizing the parts. My main concern would be corrosion, and erosion arising from cavitation, especially at very high power levels. I am wondering if stainless steel or bronze might not be a better choice of material ?

The other curious thing about this, is that the rotor is double sided, but the water inlet and vent only go to one side of the rotor. Fair enough the water will probably distribute itself evenly side to side, but I cannot see how the air can. The water completely seals the rotor to the case right around the periphery, so one side of the rotor does not appear to be vented.

A ring of very small holes between the vanes, just beyond the rotor hub, or perhaps dual air vents might remove any doubts about internal air pressure problems.

These water brakes are a really interesting bit of gear.

[Sandra]

I wonder if anyone knows how the case for the waterbrake looks like inside?? Is it a smooth or rough surface?