I am working on a project using two double acting cylinders attached to one electric pump. The cylinders do not react in sync with one raising before the other starts. The plumbing between the cylinders and pump is equal size and exact length of hose. How do I sync these cylinders without a solid connection (i.e.: loader bucket) between them?
- Thread starter EWS
- Start date
Blackhole49
Well-known Member
- Location
- White Lake MI
I'll be interested in the answers. I don't think it can be done. What are you trying to accomplish? You need equal resistance on each cylinder for the to move equal distance.
Eagle Beagle
Member
Mike(NEOhio)
Well-known Member
- Location
- Newbury, Ohio
That almost never happens. It can be done by feeding one cylinder and using the outflow from the other end to power a second cylinder. Actually two cylinders in series. The bores have to be sized so they will travel at the same rate. The rod end of the first and the base end of the second must have equal volume. Even then due to fluid bypass the second cylinder will get ahead of the first. There needs to be a valve between the second and the powered side so they can be equalized from time to time.
BarnyardEngineering
Well-known Member
- Location
- Rochester, NY
It would help to know what you're building that requires two independent cylinders to move in sync.
Maybe there's a solution to the problem outside of hydraulics that will be more reliable and predictable.
Maybe there's a solution to the problem outside of hydraulics that will be more reliable and predictable.
Traditional Farmer
Well-known Member
- Location
- Virginia
Just like electricity the hydraulic fluid will follow the path of least resistance.
BarnyardEngineering
Well-known Member
- Location
- Rochester, NY
You may need to mechanically connect the two arms of the log lifter.
Eagle Beagle
Member
75 years ago, my father-in-law built a large press. Twin 8 inch rams only running 800 psi. A rotary flow divider which was military surplus made the press work like magic. Install a 1/4 inch line with a needle valve between the two inlet ports if for some reason you need to synchronize the cylinders. That was never needed to be done the many times I used the press.
Beagle
Beagle
retired farmer
Well-known Member
You have to have a solid frame that both cylinders are attached to. You probably are trying to use them individually at each end of the log. Won't work.
Determined
Well-known Member
Guessing you have 2 separate lift arms each with it's own cylinder.
If you were to install a 2 spool hydraulic valve with one controlling each cylinder you could pull both handles to lift a log and back off on one or the other easily enough to compensate for the uneven lifting.
Eagle Beagle
Member
Rotary flow dividers are a proven design, no need for electronics, no need to reinvent the wheel! No need to modify your design- just plumb one of these in there and get to work.
Beagle
Flow divider
Beagle
Flow divider
Tx Jim
Well-known Member
- Location
- Coyote Flats, Texas
Ditto if attachment points of each end of cylinders are solidly attached together the cylinders will operate together.
My J&I flatbed with bale spears has 2 cylinders that the hoses are attached together that the cylinder rods extend/retract at same time. Another example is quick attach frame to attach bucket/bale spear to frt end loader or skid steer.
A timing rod is utilized on FEL QA to keep cylinder rods operating simultaneously.
Eagle Beagle
Member
There is no need for rephasing cylinders in this application, rephasing means the the cylinders are already out of sync. "ews" wants two identical cylinders which he already has to move out and in at the same speed with one control valve. There is no simperler way to accomplish
this than the use of a rotary flow divider. Two different size cylinders plumbed in series would work, but the larger cylinder will exert more force than the smaller cylinder. then there is the cubic inch displacement calculations the come into play with this setup.
Beagle
this than the use of a rotary flow divider. Two different size cylinders plumbed in series would work, but the larger cylinder will exert more force than the smaller cylinder. then there is the cubic inch displacement calculations the come into play with this setup.
Beagle
Eagle Beagle
Member
You don't need equal resistance on each cylinder, you need equal flow. You need the same amount of oil flowing to each cylinder irregardless of the force needed to move the load. How do you get equal flow with different pressure demands? A hydraulic flow divider provides either a mechanical link in the case of a rotary divider or a pressure equalizing spool type divider. By the time the spool divider has a chance of working, a small amount of fluid has already gone to one cylinder and after a time, one cylinder will get ahead of the other. Both dividers need a small line with a needle valve installed for those rare times recalibration is required.
Beagle
Beagle
Eagle Beagle
Member
I ment to add that spool type dividers wont work for reverse flow, one way only!
beagle
Flow Dividers
beagle
Flow Dividers
used red MN
Well-known Member
- Location
- Coon Rapids, MN
If you are using the cylinders for a loader bucket tilt then as Jim says the mechanical connection will cause the
cylinders to move together. If you have the cylinders doing independent tasks which ever one requires the least
amount of PSI to do it’s task will move first. What wore out is suggesting may work for what you are trying to do
if it is not the loader bucket you gave as an example. You will need some amount of “engineering” to figure out
the cylinder sizes you need. And they will have to be made for rephasing by having bleeds at the end of their
stroke to get trapped air out.
cylinders to move together. If you have the cylinders doing independent tasks which ever one requires the least
amount of PSI to do it’s task will move first. What wore out is suggesting may work for what you are trying to do
if it is not the loader bucket you gave as an example. You will need some amount of “engineering” to figure out
the cylinder sizes you need. And they will have to be made for rephasing by having bleeds at the end of their
stroke to get trapped air out.
bradley martin
Well-known Member
Eagle beagle has the correct answer! A rotary flow divider is the answer.
Brendon-KS
Well-known Member
- Location
- Goessel, KS
Eagle Beagle's suggestion of a rotary flow divider would be the only practical solution in order to make the parts you have on hand currently work in your application if adding a solid connection between the cylinders isn't feasible. The other option you could consider is replacing one of your existing cylinders with a different one of appropriate size to set up a master/slave arrangement. As others have said the rod end piston area of the master must match the base end piston area of the slave in order for them to move at the same speed. The master should have a rephasing groove at full extension so you'd need your new cylinder to be sized as the master.
If you go with the rotary flow divider option be sure to get one that is sized appropriately for your pump's outlet flow. Bigger isn't better in this case since if the input flow is too low the metering will not be accurate - the faster the gears are spinning the more accurate the flow division will be. So, you'll want to choose one that has your pump's flow rate towards the upper end of its specified input flow range.
If you go with the rotary flow divider option be sure to get one that is sized appropriately for your pump's outlet flow. Bigger isn't better in this case since if the input flow is too low the metering will not be accurate - the faster the gears are spinning the more accurate the flow division will be. So, you'll want to choose one that has your pump's flow rate towards the upper end of its specified input flow range.
Dan in North Houston
Member
As others have pointed out, the cylinders will lift unevenly because the friction / resistance is never equal.
I am not familiar with rotary flow dividers as others have mentioned, but one thing that I have not seen mentioned is that each log is going to be a different weight, and the heavy end will not always be x% heavier than the light end. Will a rotary flow divider work in this case?
If you can't link the two cylinders together to get even lift, perhaps a separate control for each cylinder to allow you to equalize it yourself might be a simple fix.
I am not familiar with rotary flow dividers as others have mentioned, but one thing that I have not seen mentioned is that each log is going to be a different weight, and the heavy end will not always be x% heavier than the light end. Will a rotary flow divider work in this case?
If you can't link the two cylinders together to get even lift, perhaps a separate control for each cylinder to allow you to equalize it yourself might be a simple fix.
Eagle Beagle
Member
Yes Dan, it would work perfectly. A rotary flow divider is nothing but two sets of gears connected by a common shaft. I you were to take two identical gear pumps and drive them from a common shaft, then would not the flow from each pump be identical? Remember that the speed of a cylinder or motor is a function of flow. Pressure is the result of resistance against the flow. In the case of the rotary flow divider, both cylinders would react the same if one side of the circuit exhibited more resistance.
The maximum resistance would be determined by a relief valve upstream from the rotary divider. This can best be pictured as two control valve handles welded together on a two spool valve.
Flow or gallon per minute, is what controls the speed---
pressure or PSI is a measure of force needed to overcome the load!
Fellow texan here Dan! Up DFW way.
Beagle
The maximum resistance would be determined by a relief valve upstream from the rotary divider. This can best be pictured as two control valve handles welded together on a two spool valve.
Flow or gallon per minute, is what controls the speed---
pressure or PSI is a measure of force needed to overcome the load!
Fellow texan here Dan! Up DFW way.
Beagle
Eagle Beagle
Member
In a case where you have two identical cylinders with the oil being introduced to the base end of the first cylinder and then the oil from the rod end going to the base end of the second cylinder, the second cylinder would only rise part way do to the discrepancy in the volume of oil in the rod end of the first cylinder vs the base end.
The diameter and length of the rod inside of the cylinder need to be accounted for as it occupies the same space as the oil. I'll wager your wings on on the cultivator lift fairly even do to the weight be lifted is almost equal.
Beagle
The diameter and length of the rod inside of the cylinder need to be accounted for as it occupies the same space as the oil. I'll wager your wings on on the cultivator lift fairly even do to the weight be lifted is almost equal.
Beagle
Brendon-KS
Well-known Member
- Location
- Goessel, KS
"but the larger cylinder will exert more force than the smaller cylinder"
This is actually not correct although on the surface it appears that it would be the case. The smaller diameter slave cylinder can lift just as much as the larger master because the pressure being applied to it is proportionally greater than that on the master (assuming they are properly sized to run in sync with each other). For example, say you have a 3.0" bore, 1.25" rod cylinder as the master and a 2.75" bore cylinder as the slave (one of numerous size combinations that play well together for master/slave systems) and a 2000 psi pump relief. If the master is raising a load with none on the slave you'd have a maximum force of 14140 lbs (2000 psi times 7.07 sq inch). Now if the slave was lifting a load by itself you need to take into account the pressure increase happening across the piston of the master cylinder. Here you'd have 2000 psi at the master base but due to the ratio of the areas on the base and rod sides of the piston you'd have 2420 psi being supplied to the base of the slave. Multiply this by the base area of the slave cylinder (5.94 sq inch) and you get essentially the same 14140 lbs maximum force as we calculated for the master. (The math is slightly different because no master/slave system using off-the-shelf cylinder diameters is perfect. In our example here the mismatch between the two cylinders is less than 2% which is close enough for most any practical usage.)
This is actually not correct although on the surface it appears that it would be the case. The smaller diameter slave cylinder can lift just as much as the larger master because the pressure being applied to it is proportionally greater than that on the master (assuming they are properly sized to run in sync with each other). For example, say you have a 3.0" bore, 1.25" rod cylinder as the master and a 2.75" bore cylinder as the slave (one of numerous size combinations that play well together for master/slave systems) and a 2000 psi pump relief. If the master is raising a load with none on the slave you'd have a maximum force of 14140 lbs (2000 psi times 7.07 sq inch). Now if the slave was lifting a load by itself you need to take into account the pressure increase happening across the piston of the master cylinder. Here you'd have 2000 psi at the master base but due to the ratio of the areas on the base and rod sides of the piston you'd have 2420 psi being supplied to the base of the slave. Multiply this by the base area of the slave cylinder (5.94 sq inch) and you get essentially the same 14140 lbs maximum force as we calculated for the master. (The math is slightly different because no master/slave system using off-the-shelf cylinder diameters is perfect. In our example here the mismatch between the two cylinders is less than 2% which is close enough for most any practical usage.)
Tx Jim
Well-known Member
- Location
- Coyote Flats, Texas
Simpler is usually better. Thanks for update
Destroked 450
Well-known Member
- Location
- Harned, Ky
That was a good choice.
I've worked around and built a few production saw mills, for log handling mechanical connection is the best and safest way to go.
A rotary flow divider will work just fine but if a hose blows to one cylinder the log will come back down on one end possibly spinning it sideways with it possibly coming down on something or someone.
With mechanically connected loader arms if one line blows you may lose lifting power but still have full control of lowering the log back down safely in it's correct position.
Dan in North Houston
Member
thanks for the explanation, I can see now why they would work in this situation. I never cease to be amazed at what I can learn here.
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