# Dump fluid?



## leigh (Jan 2, 2009)

My dump is painfully slow going down in cold weather (gravity) Whats a good weight fluid to use?


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## basher (Nov 13, 2004)

do you have a return filter?


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## leigh (Jan 2, 2009)

basher;1893194 said:


> do you have a return filter?


I'll look.Got to be the most overlooked maintenance items!


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## White Gardens (Oct 29, 2008)

Electric over hydraulic, or standard central hydro system? 

Iso 32 is good for colder temps. 


.......


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## leigh (Jan 2, 2009)

White Gardens;1893267 said:


> Electric over hydraulic, or standard central hydro system?
> 
> Iso 32 is good for colder temps.
> 
> .......


Electric..


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## White Gardens (Oct 29, 2008)

leigh;1893286 said:


> Electric..


Did you look at the filter?

.....


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## leigh (Jan 2, 2009)

White Gardens;1897244 said:


> Did you look at the filter?
> 
> .....


Not yet,dealing with replacing exhaust manifold gasket!


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## TJS (Oct 22, 2003)

I have an adjustable valve on my pump (gravity down) because I had to slow it down originally because my headache rack is heavy and the weight caused it to go too fast. I adjust my valve in the winter to attain the same down speed when it is warmer out. Some of these pumps have a set orfice size in them to prevent coming down to fast. You can remove them and put an adjustable one in place with a knob. I use the SAM blue fluid all year. Not a problem. My pump is not in the elements though. It is in my side box for some extra protection.


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## leigh (Jan 2, 2009)

Thanks......


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## SnowGuy73 (Apr 7, 2003)

I always ran aircraft hydraulic fluid (blue thin stuff) in mine.


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## Aerospace Eng (Mar 3, 2015)

SnowGuy73;1897363 said:


> I always ran aircraft hydraulic fluid (blue thin stuff) in mine.


I know it's really old, but for what it is worth....

There are several types of aviation hydraulic fluid.

Blue - Castor oil and alcohol, should only be used in systems with natural rubber seals. Obsolete prior to WWII.

Mineral-oil based....

Mil-PRF-5606 (Most piston prop aircraft since the 1930s, some bizjets and turboprops)
Mil-PRF-83282 (Fire resistant replacement of 5606, most bizjets and turboprops)
Mil-PRF-87257 (Addresses some low temperature viscosity issues with 83282)

All of the above are dyed red.

5606 and 87287 have a viscosity of about 50 Centistokes at 0C, while 83282 is about 75 Centistokes at 0C.

The other type is a phosphate-ester base, and has been used in commercial jet aircraft since the late 1950s. It is fire resistant, but is more expensive than mineral based fluids. There are a few different types, but generally are called "Skydrol." All versions of Skydrol are a purple color. Without trying to enumerate all the grades, Skydrol is about 40 Centistokes

More importantly, Skydrol is completely incompatible with mineral based fluids, and Skydrol is incompatible with seals that are compatible with mineral based fluids and vice-versa.

If you need a thinner fluid and your system was designed for mineral based fluids, get a thinner iso grade, don't convert to Skydrol.

ISO 32 at 0C is about 400 Centistokes.

Note that a standard temperature for rating oils is 40C (104F), and mineral oils get about 7-10 times thinner as the temperature is raised form 0C.

Pumps from different manufacturers and different models within a manufacturer will have different viscosity requirements.

Bosch, for example, 
Rotary Piston pump 10 min, 21-54 optimum, 65 max cont, 162 startup.
Gear Pump 12 min, 20-100 optimum, 800 max cont, 2000 startup.
SV-80 Vane Pump, 32 min, 43-65 optimum, 216 max, 864 startup

If your pump is engine driven and turns all the time I would be careful about changing the viscosity too much, since the fluid in the pump (and valve body and intermediate lines) will be constantly circulating and will warm up while the fluid stagnant in the dump bed will be cold and thus have a different viscosity. If the viscosity at the pump is too low, the pump (and likely the valve bodies) will experience premature wear, and suffering with a slow bed may be preferable to buying a new pump.

One alternative would be to use pipe insulation or something similar on the lines to/from the cylinder and valve body and insulate the cylinder itself. Once the pump has circulated for a while, raise and lower the bed a few times to get warm fluid into the cylinder.

If, as indicated in one of the posts, the pump is electric, and is only on when the bed is moving, then a thinner fluid for the whole system might be warranted. Figure out from the pump manufacturer what viscosity the pump is designed for. Just remember to change it out when temperatures rise to the point where you would be too thin for the "Optimum" range.

Due to different requirements for different hydraulic system designs, an understanding of the hydraulic system is required to give a valid answer.


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