Reducing flow and pressure in hydraulic branch circuit

[jimmysisson]

I would think the little flow restrictor washers inserted in the fittings at each cylinder would do your job. I made a couple at home, experimented with the hole size (starting maybe at 1/16") and slowed my log lift down so it's manageable. You're right about the catapult part!
I divided the flow with an adjustable proportioning valve but removed it after finding the adjustments were just too fine. I agree with JJ that heat won't be an issue due to the infrequency of moving these accessories.
Jim

 

[Scooby074]

Jim, as it stands right now, restricting orifices (washers) are the plan. :thumbsup:

 

[glastron23]

Hi Scooby ... can't understand why HS couldn't help you, these guy's know their stuff, restricting the cylinders will do the job, just one thing that people should be careful of is restricting out flowing oil especially when it is on the rod end of the cylinder. The volume of oil leaving the cylinder can be pressurized to a very high pressure if restricted, you should use a cartridge that has free a flowing exhaust circuit...
Sun Hydraulics - Cartridge - NCCD
your application will be ok but a cylinder with a big base and no weight on the rod can be trouble... check out the video.... Jim Pressure intensification caused by meter-out flow control

 

[Scooby074]

Hi Scooby ... can't understand why HS couldn't help you, these guy's know their stuff, restricting the cylinders will do the job, just one thing that people should be careful of is restricting out flowing oil especially when it is on the rod end of the cylinder. The volume of oil leaving the cylinder can be pressurized to a very high pressure if restricted, you should use a cartridge that has free a flowing exhaust circuit...
Sun Hydraulics - Cartridge - NCCD
your application will be ok but a cylinder with a big base and no weight on the rod can be trouble... check out the video.... Jim Pressure intensification caused by meter-out flow control

Thanks.

The HS guys are good. They just couldnt get me the prince priority valve i wanted. This was prince's fault. Prince said 6 weeks.

Im going to call HS likely tomorrow and get a price on some Parker hose. If theyre close in price to Princess ill get it there instead of the cheaper Ryco hose from princess.

I dont think im going to use the needle valves you linked to. Im just going to go with a fixed orifice. Its cheaper. And i dont anticipate needing to change the flows once i find a flow that works. If the restriction is on the base of the cylinder it'll work for for extraction, but what about retraction? I dont want to intensify the pressure on the base end. Are fixed orifices available with checks so they bypass so i dont meter out?


Edit: Bosch Rexroth makes one Pn. 04.46.03.00-Y-Z. Thats in 1/4 and i need 1/2http://www.oilcontrol.com/website/archive/interactive_catalogs/sleeve/template/pdf/04460300YZ.pdf So im sure there are others. Just a question of price and availability.

Any suggestions for a cheap way to restrict flow if the above orifices arent available? I need to restrict both directions of movement on 2 cylinders. Thats 4 needle valves with check if i avoid a meter out situation!! Too much $$


/ EDIT: If my math in post 26 is correct, a restricting orifice in only the base end of the cylinder should work for flow control. No reverse checks should be needed?

 

[glastron23]

Scooby.. princess auto have these in stock, will give you a lot of adjustability http://www.princessauto.com/power-t...8322968-15-gpm-adjustable-line-throttle-valve
but no bypass. the intensification should be low as the rod end area is small, can be checked with the installation of a psi gauge between the cylinder and throttle valve

 

[Scooby074]

There will be next to no weight on the cylinders (maybe 50-100Lbs max) on the return stroke. So the only intensification will be the cylinder ratio . Is this correct? Im going to try and do the math on this. Cylinder is 2.5" bore with 1.125" rod.

rod end area is 3.912 sq in.

Base piston area is 4.909 sq in

100lbs / 4.909 = 20.371 psi.

So there is 20.371 psi on the return stroke just from the weight of the log lift.



3000 psi (rod, max system press) x 3.912 (A rod) = 11,736 LBS force on the rod end.

11815 lbs / 4.909 (area of base piston) = 2,390 PSI + 20.371 PSI(weight of lift) = 2410 PSI On the base end

2410PSI on the base end of the cylinder? This is at rest and assuming a plugged orifice at the base. That cant be right?" ... If thats correct i should have no issues with increasing the pressure on retraction as ill never end up with much more than 2500 PSI on the base side of the piston. The orifice will result in less pressure than the dead headed worse case scenario.

SO I SHOULD BE OK WITH A SINGLE FIXED ORIFICE ON THE BASE END OF THE CYLINDER? In other words a metering situation during retraction. Is this correct?????

(yes i did the calc the long way... just had to think it though )

 

[Scooby074]

Now the question of a good starting point for a fixed orifice.

This is harder math. LOL.

Pump is 22gpm. 3000 PSI. Hoses are 1/2. Cylinders are 2.5" with 1.125" rod. 2 NPT 90's per run, so 4 total for the loop. Probably ISO32 hydraulic fluid.

Id like them to see about 2 GPM to have a reasonable extension speed (3-4 sec).

Formula i found for the diameter calculation is

D= .23 * sqrt ( Q / sqrt (delta p) )

D= 0.23 sqrt ( 2 GPM / sqrt (1 PSI) )

D= 0.32"

Im not sure thats right. Particularly the pressure drop part of the calc. Is 1 PSI drop reasonable for this calculation I dont believe it is? Can anybody shed some light?

 

[J_J]

I am not to sure about your figures. The two stage pump will pump 22 GPM at about 650 psi, and about 7 GPM at 3000 psi.

If you add restrictors inline, the cyl may be working at the slow speed and high pressure. If the cyl are not pushing much of a load, they could work at the fast speed and low pressure.

You may be forcing the cyl to work slower just using the restrictors.

 

[Scooby074]

I am not to sure about your figures. The two stage pump will pump 22 GPM at about 650 psi, and about 7 GPM at 3000 psi.

If you add restrictors inline, the cyl may be working at the slow speed and high pressure. If the cyl are not pushing much of a load, they could work at the fast speed and low pressure.

You may be forcing the cyl to work slower just using the restrictors.

yes, i wondered about the pump shifting to high press during the lift.

ugg.. :mur:

 

[slowzuki]

You shouldn't use a restrictor to slow a fixed displacement pump down. Shifting it to low is is fine but purposely forcing the pump to go into relief is bad design.