Hydraulic tank/reservoir cap

[tirebiter]

I'm a newbie at this. Bought an old (1948), very used CASE 400 diesel tractor to mow a couple of small fileds and help with snow removal here in Southeastern New England. Is it normal that when the hydraulic tank/reservoir cap is loose, the hydraulics all get really weak and slow ? I have to tighten the screw-on cap (Pipe thread) with a stillson wrench to get the hyrdraulics to work at what seems normal speed. When I loosen the cap, there is a lot of pressure that takes several minutes to bleed off. After the pressure is equalized the hydraulics are very slow again and generally speaking, work very poorly. I think the front-end loader and three-point-hitch hydraulics may have been an add-on when it was new. I'm not getting very far looking online for info about this tractor and thought maybe someone here could help fill me in on some. Thanks for any help any of you may have.

 

[J_J]

In general, there should be no reason to pressurize the hyd tank.

It must also have a vent to let heat escape.

Your pump and the resistance to the pumped fluid is what generates pressure.

If the pressure is weaker that original, then it is from wear, faulty relief valves or weak seals on the cyl.

Cold fluids tend to have better compression,and warm/hot fluids flow more readily, and will pass through imperfections, resulting with less pressure.

 

[Leejohn]

See if there is a screen in the tank or a filter on your intake line. If so clean or replace.

 

[IceStationZebra]

Pressurized reservoirs are sometimes used to prevent pump cavitation. I don't know anything about Case tractors, but I've never heard of a pressurized reservoir in a tractor.

ISZ

 

[Farmerford]

You are my kind of man: 1948 Case and still call a pipe wrench a "Stillson Wrench", named after the fellow who invented it in the mid-1800's.

LeeJohn probably explained the problem. If there is a wire mesh screen inside the tank that protects the suction line from debris, it is probably stopped up with 65 years of trash. So, the supply of fluid to the pump is largely blocked. That means the pump is cavitating and the entrained air in the fluid expands into small bubbles. That increases the total volume of fluid and air in the system, which accounts for the increased pressure in the tank. But the increased pressure also increases the amount of fluid that flows through the partially blocked screen, so the pump moves more fluid when the tank is closed than when it is vented. That's why the hydraulics are faster when the tank is sealed. But sealed or open, the pump is cavitating, and cavitation is very bad for the pump.

The screen is probably on the inside of the pipe fitting that screws into the suction fitting on the tank. Remove that fitting and you will probably find a clogged screen.

 

[tirebiter]

Thanks everyone and particularly Farmer Ford. I have been getting LOTs of foaming/emulsion. I was making what seems to be an incorrect assumption it was due to running low on hydraulic fliuid and the pump sucking in some air when the tractor was on an incline (steep driveway to clear the snow from). I'll have a look for a pump intake screen/filter. If it's clogged, that would explain a LOT. I was also thinking the tank may need to be pressurized if the pump was incapable of lifting fluid, even though the pump is only about one foot higher than the top of the tank.

I'm hoping the leaks at the spool valves that are also plaguing the tractor will become reduced or stop also with zero residual pressure in the system when the tractor is parked. I understand the need to have a vent to allow for thermal expansion. All I can spot for venting is a small hole in the rear cover for each spool valve.

I'll post my findings in a day or so.

 

[J_J]

Spool valves are not designed to vent.

If you see fluid leaking at the spools, any seals on the spool are bad. Some spools have no o-rings, just precision fit for seal.

Several things can cause air in fluid.

Pump cavitation, suction leak, relief valve used to much will cause cavitation and heat.

So an open vent on tank is a good thing.

If you install a 3000 psi hyd gage in the system, you might get a warning that things are happening, and further more, it will allow you to do some observation and trouble shooting about your hyd system.