Hydraulic Question-Restricted Orifice Fitting

[LEES WOODC]

Ok before the problem gets any worse: or if you have a blown hose or get hurt


You need one-two way needle valve(restricted flow in, free flow out) on the barrel side of the cylinder to solve your problem period!!!!!!!!!!


You are blowing oil across the relief valve after the pumps drops into the lower stage and that adds air and heat to the oil-not good with a small tank.

The oil is cavitating and hammering against all the surfaces in the hydraulic system.

leon

opcorn:

I have a truck with a restrictor in one of the cyclinders and until I learned to idle the engine during this cycle I was blowing hoses like crazy.Leons right about the two way needle valve. Your going to blow a hose in front of that restrictor and get oil all over everything if not in your bloodstream or take an eye out. Your messing with powerful stuff putting a restrictor inline.

 

[Bl8tant]

So what IS the proper application for a restrictor fitting? They must be common since I bought mine at TSC and they don't ever have anything that's specialty.
Where might one find a restricted orifice in everyday hydraulic systems and why don't they have issues?

 

[kevin j]

Short on time, death in the family and upcoming wedding, so this is low priority right now!

for intermittent use, they can work fine.
Misc notes:
-Not nearly as simple as it looks, You may get lucky and work jsut fine, but may create some undesireable pressure effects too.
-Without getting into the math, to control a load you 'normally' want flow control on the outlet of the cylinder. This is called 'meter out flow control'.
The load is always being hedl bqack by the oil in compression.
Controlling an overruning load by 'meter in flow control' means the load can run away and the cylinder cavitates. But with meter out, you have to watch out for intensification, where the incoming pressure times bore bore area creates a higher pressure in the outlet or rod side.
-For a lift, one direction load only, you could meter into the lift direction. Then, on the down direction the same orifice creates meter out control. Fixed orifice in both direction can cause some pressure problems.
Not easily explained quickly here. I would use a flwo control with reverse free flow. They look like a micrometer knob on the side. Controlled one way, free the other. May need two of those, one on each side.
-
-How about limiting the stroke of the spool valve with springs or shims in the end cap? Dependn on the valve this can work well.

-Since the pump is constant flow, (either high or low gpm) the pressure will build until the pump shifts into low gpm. If this is over 800 psi or whatever your unloading setting, and the 2 gpm or whatever flow matches the orifice, great just lucky. If not, the excess flow goes across the relief valve at 2500 psi or 3000 psi or whatever. So your pump will see the RV setting, just like it does at end of each stroke. No big deal, you won't blow any hoses. However, If you put an orifice on the pressure hose before the RV, then you will very likely blow a hose or pump. You for sure need the relief valve between pump and orifice.
Don't do this for continuous use, like a motor, as the heat buildup would be terrible.

I can look at the math later if you have cylinder dimensions and the load or operating pressure it is lifting in both directions.

k

 

[Bl8tant]

Kevin - Thank you. Your post made it clear to me what folks were concerned about. In my case, the resticted fittings were "after" the RV so I don't think there was any danger. I installed them in the working ports of the valve inline with the hoses going to the cylinder.

BUT..I decided to go ahead with Plan "B". I already have a fortune tied up in fittings, so I just drilled out the orifice fittings to a larger size. The hole was initially about 1/40". I drilled them out to 9/64". I have not fired it up to test, but I suspect that going that much larger probably rendered them nearly full-flow. The needle valve would have been nice, but they are expensive considering what they do. I also did not have enough clearance to mount one anyways.

Once I get everything done, I was thinking of starting a new thread with pics to gauge response to the "sliding beam mod". I think a lot of folks have avoided this thread due to the technical-sounding nature of the title.

Thanks to all who posted.