Consistency with hydraulic speed, fluid VI help? 1

[lankeeyankee]

HI I am new to the forum and been pulling my hair out trying to resolve this issue I have with inconsistent hydraulic operation. I figured I would go to the pros which is the forum boards and here I found you guys / gals.
My application is being used on a hydraulic clutch system, which is on a motorcycle, which is being used for bracket racing.
The problem I am having is. The clutch speed is varying as much as .080 of a second with the temperature change. This is causing me problems! The temperature range its working in is 80F to 165F.
Originally it was using DOT 3-brake fluid. Someone told me to try DOT 4. Well using DOT 4 caused the problem to get worse.
I have been reading about mineral oil which has a high VI rating which is supposed to be less sensitive to change in temperature?

OK here is what’s going on.
Operating temp range = 80f to 165f
Travel of stroke on hydraulic = 1in
Duty Cycle 2X’s on an avg. of every 30 mins.

I am wanting to know what would be the best fluid to use that wont have the drastic change on hydraulic speed with the temp ranges I am working in? A light weight mineral oil? What brand?

Donn

 

[MikeHalloran]

There may be an orifice in the system that's supposed to slow the clutch release, e.g. when you 'sidestep' it. Its operation is probably sensitive to temperature more than any other component in the system.

Find it and drill it out a little, or a lot. Removing it will make the bike much easier to stall, or harder to not stall, depending on your perspective.





Mike Halloran
Pembroke Pines, FL, USA

 

[lankeeyankee]

I am sorry I forgot to mention all the devices.
Master Cylinder to a steel braided hose to an adjustable flow control to a 12VDC line lock solenoid to a steel 1/8 line to the slave cylinder.

 

[hydtools]

Why the flow control? Control clutch engagement?
Flow controls may be viscosity sensitive since they depend on pressure drop across an orifice.
Mineral oil is not a high VI oil. Look into hydraulic fluids for high VI fluids.

It may be nutty, but water viscosity does not change noticeably at those temperatures. Might be worth testing just for benchmark performance.

Ted

 

[lankeeyankee]

Hi Ted

Yes the flow control works how fast the clutch disengadges. Its on a motorcycle.
I am basically needing a fluid that will work the slave cylinder and minimize the difference of .080 with temp change.
Back to back runs its deadly consistent down to .005!
Will a real thin wt. mineral oil be an improvement over the dot 3 brake fluid? I am not really worried about the weight just as long as its consistent in the temp range I am working with.

 

[MikeHalloran]

See if you can find a >temperature compensated< flow control.

Such things exist for industrial hydraulic systems, to deal with exactly the problem you report. If your flow control is a simple 'motorcycle' part, you may be SOL.

.. unless you want to add a temperature sensor controlling a solenoid valve that opens another flow control in parallel with the existing one, or something like that.



Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

... which is to say, you're not going to find a magical hydraulic fluid that will solve the problem. You have to compensate some other way.





Mike Halloran
Pembroke Pines, FL, USA

 

[lankeeyankee]

Thanks Mike

All the components are industrial, no such thing as going to the motorcycle store and asking for a hydraulic flow control and a mac valve.
I will do some searching on the temp sensing flow control. I was hoping that using something besides dot 3 brake fluid would be less sensitive to tempature.
So what your saying is using a thinner type of fluid with a higher VI wont help with the inconsistency?
If I could just get it from .080 down to .025 I would be satisfied. I purchased some mineral oil light weight so I am hoping that this improve the issue

 

[hydtools]

Go with a lighter, thinner oil. There will still be a temperture effect, but the viscosity change will be over a range of lower viscosities and your max time will be lower.

Ted

 

[lankeeyankee]

What is the lowest viscosity I should run in this application?
Since its for a clutch rather then a brake there is no high temps to deal with and also its not constantly being acuated.
I am guessing mineral oil, what is the lightest / thinest I can purchase and do you have a name brand?

 

[hydtools]

Try automatic transmission fluid, ATF. It has a very low viscosity and generally high VI.

Ted

 

[romke]

the viscosity of an ATF, although low, is far higher then DOT3/4 brakeluid. That therefore might worsen the problem.

You should also be aware that you cannot use a mineral oil in a brake system designed for use with DOT3/4 brakefluid. Using mineral oil in such a system would result in iantic seal swell and immediately destroy all the seals.

I you would like to use a mineral oil you will have to change all the rubber seals in the system to a material compatible with mineral oil. If you do I would advise trying the socalled LHM brakefluid - a low viscosity mineral oil based synthetic brake fluid as used in certain Citroen cars. You may also look out for a mineral oil based brake fluid according to ISO 7803 - which is actually the same fluid. That kind of luid has a viscosityindex of about 300.

Another possibility would be to change over to a DOT 5 luid. That also would make a change in sealing materials necessary, since DOT 5 luids are silicone based, whereas DOT 3/4 are based on borate esters. The advantage of a DOT 5 luuid would be a significant lower viscosity compared with either DOT 3/4 or ISO 7803

 

[hydtools]

The ATF will not worsen the problem if its viscosity does not change as much as brake fluid. The flow control may have to be adjusted for the ATF.

The application is a clutch system not a brake system.

The VI of 300 of the LHM brake fluid is a good thing. The VI of ATF is in the 190s

Ted

 

[EdDanzer]

Part of your problem may be the 1/8” line. Before changing fluids try upping the ID of all the lines and fittings. Gates has a fluid flow calculator

http://www.gates.com/industrial/pressure/fluidFlow.cfm?location_id=3044

You may need to register to use it. This tool allows you to use different fluids to see the flow velocity differences with different ID items.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[lankeeyankee]

Thank you everyone for all your input.
Well I tried my new setup this weekend. I went to my local hydraulics shop to have a different configuration made up I brought my whole system.
Master Cylinder (What forces the fluid.. those not familiar with motorcycles.
Stainless braided hose.
Flow Control
Solenoid lock valve.
Slave Cylnder (Is what forces the clutch rod)

Orginal setup
Master cylinder.
Steel line 26 inches long
12VDC line lock solenoid
Flow control
1/8 steel line to slave cylinder.
DOT3 brake fluid.

New Setup
Master Cylinder
Flow Control attached to master cylinder.
13inches of steel line
12VDC line lock solenoid
13 inches of steel braided hose
Slave Cylinder.
Mineral Oil

Well i tried the new setup this weekend.
Samething When the sun went down I had to remove .060 from the delay timer to achieve the same reaction times. It was consistent with the sun setting?

OK I am not worried about viscosity, I dont care if its as thick as syrup or as thin as water. I need a fluid that isnt effected by tempature or a setup? Or if its even possible with hydraulics?

How about 6:1 synthetic fluid used in German automobiles for antilock brakes? Or is there a fluid out there that doesnt change flow with just 20f in temp change?

Thanks.

 

[hydtools]

Try Mil-H-5606 hydraulic fluid, aircraft hydraulic fluid. It is used in bucket trucks (cherry pickers), too.

Like Danzer recommended, increase the line size from 1/8" to reduce losses when the sun goes down.

Ted

 

[romke]

whatever fluid you use, the viscosity will change quite considerably when the temperature changes. even over the small temperature range (85 / 47C) the viscosity changes with a factor of 2.5 or more, depending on the viscosityindex of the fluid. The factor 2.5 applies to a fluid with a VI of about 330, most fluids are a lot more temperaturesensitive.