Fast extend hydraulics.

[J_J]

Why is fast extend faster.

Because if you add the GPM's from the pump and the GPM's from the rod side, the total GPM's forced into the cyl will make it faster. GPM's determines the speed of operation.


4 in cyl
2 in shaft
24 in stroke

Volume of fluid extended - 1.305 gal
------------------retracted - 0.979 gal

1 GPM flow

Extend time - .3 ips - 80 sec
Retract time - .4 ips - 60 sec
Total cycle time - 140 sec
Fast extend time - 34.28 sec

10 GPM flow

Extend time - 3.1 ips - 7.74 sec
Retract time - 4.1 ips - 5.85 sec
Total cycle time - 13.59 sec
Fast extend time - 3.3 sec

Someone double check my figures, I could be wrong

 

[oldnslo]

Why is fast extend faster.

Because if you add the GPM's from the pump and the GPM's from the rod side, the total GPM's forced into the cyl will make it faster. GPM's determines the speed of operation.


4 in cyl
2 in shaft
24 in stroke

Volume of fluid extended - 1.305 gal
------------------retracted - 0.979 gal

1 GPM flow

Extend time - .3 ips - 80 sec
Retract time - .4 ips - 60 sec
Total cycle time - 140 sec
Fast extend time - 34.28 sec

10 GPM flow

Extend time - 3.1 ips - 7.74 sec
Retract time - 4.1 ips - 5.85 sec
Total cycle time - 13.59 sec
Fast extend time - 3.3 sec

Someone double check my figures, I could be wrong

JJ,
My math shows fast extend for 1 GPM would be 1.22 IPS or total time of 19.51 seconds.

at 10 GPM extend time would be 1.95 seconds.

Way I am figuring this is:

On regen or fast extend circuits the pump flow is only filling the rod area or in this case a 2" diameter.

1 GPM will extend a 2" diameter at a velocity of 1.23 IPS or 73.53 IPM

1.23 IPS for 24" stroke = 24 / 1.23 = 19.51

formula I use is Q = VA
Q= flow in cubic inches per second. GPM x 3.85 = cubic inches/sec
A= area in square inches
V = velocity on IPS

Some one better check my numbers also. Pretty significant difference from JJ to mine.

Roy

 

[J_J]

Piston Dia ----- --4 in
Rod - -------------2 in
Length ----------- 24 in
Effective area - 12.57
GPM - -----------1
Extend time ---78.36 sec

Volume base -- 1.31 gal
----------rod -----.98 gal

Fast extend

Total volume from rod side and pump is now 2.29 Gal

Extend time - 34.07 sec

At 10 GPM, the fast extend time will be 3.44 sec

I think.

Check your fig again, you could be right, and I will change mine.

Roy, I think you forgot to add the rod side fluid to the pump fluid.

 

[oldnslo]

JJ,
while extending in the regen mode all the pump flow is doing is filling the volume taken up by the cylinder rod which in this case is 75.4 cubic inches

Total oil volume required to extend this cylinder is 301.6 cubic inches

Total oil volume in the rod end when fully retracted is 226.2 cubic inches. We agree that this volume is being directed to the blind or cap end during extend.

301.6 - 226.2 = 75.4

1 GPM = 231 cubic inches/minute

231/60 = 3.85 cubic inches/second

75.4/3.85 = 19.59 seconds

Roy

 

[RodNH]

JJ,

You can't just add the total base and rod side volumes together. You would wind up with more volume than the cylinder holds in any position. You also cannot just add the total rod side volume to the pump flow. That is like adding apples to oranges. They are different units. The pump flow is a rate (volume per unit time) and is dependent on time. The rod side total volume is just volume and is not dependent on time.

Roy is correct. Just use the rod area times the stroke for the needed volume in a regenerative (fast extend) mode and divide it by the pump flow, in correct units, to get the extend time in seconds.

Rod

 

[J_J]

I was skeptical of my figures, and you and Roy are right.

Please ignore post #1 and 3 as I used incorrect figures.

I am still trying to figure out how they get 25 GPM using only 4 GPM in a regen circuit.

If someone can explain it, please do.

 

[165masseyky]

I was skeptical of my figures, and you and Roy are right.

Please ignore post #1 and 3 as I used incorrect figures.

I am still trying to figure out how they get 25 GPM using only 4 GPM in a regen circuit.

If someone can explain it, please do.

I bought one of the prince 3060 valves it is a lot faster but I am unsure there numbers are correct. It seems to me the extend time should be much faster than a little more than half.


BTW here is a good calculator for hydraulic http://www.baumhydraulics.com/pages.php?pageid=4s

 

[RodNH]

JJ,

I don't know what post you are referring to regarding getting 25 gpm from 4 gpm and I haven't searched for anything. But here's my take on such a premise:

The ratio of piston rod area to piston area should be the same as the ratio of regen extend time to regular extend time. In your example of a 4"x24" cyl w/2" rod, the ratio of piston rod area to piston area is 1/4 (3.14/12.57) and the ration of regen to regular extend times is also 1/4 (19.6/78.4 for 1 gpm). That gives the appearance of a pump flow that is 4 times greater when in regen mode.

Similarly, any cylinder with a rod to piston area ratio of 0.16 (4/25) would make a 4gpm pump appear to be a 25 gpm pump when in regen mode. Using a 2" rod diameter, a piston diameter of 5.0" would meet this ratio. Such a cylinder with a 24" stroke would have a regular extend time of 30.6 sec and a regen time of 4.89 sec, both with a 4 gpm pump flow. The regular time is 6.25 times the regen time, thereby making the 4 gpm pump appear to be a 25 gpm pump (4x6.25). It's not really, of course. It just appears like one as far as cylinder extend speed goes.

The cylinder effective push force is decreased by the same factor as the speed is increased when in regen mode. This is an important fact to consider before using a regenerative circuit to increase extend speed.

Rod

 

[J_J]

This is what the specs have for the LSR-3060


STANDARD FEATURES
• Hydraulically balanced, hard chrome plated spool
• Handle can be installed in “up” or “down” position
• Extend flows of up to 25 GPM with inlet flows of 4 GPM
• Relief valve adjustable up to 3500 PSI
• Tandem center spool
• Manual shift from high speed mode to high force mode
• Spring center 4 position spool with

 

[RodNH]

The key wording in those specs is "up to". The 25 gpm is a typical maximum rating for 3/4 ports and hoses to keep pressure drops to reasonable values. The valve itself doesn't determine what apparent extend speed is obtained. That depends only the cylinder dimensions. The valve is just a standard valve with a fourth position (regen) that directs the pump flow to both cylinder ports at the same time. The oil from the rod side is directed back to the valve where it is combined with the pump flow and directed to the piston (base) side. This combination however must be analyzed on a rate basis to keep an apples-to-apples comparison. Unfortunately, the rate at which oil from the rod side is added to the pump flow rate at the valve is, itself, dependant on the cylinder speed. I suppose one could set up an equation where the rod flow is a time-dependant variable and solve for the extend time. I have not tried that but think it would just serve to complicate things. Plus, the actual flows between the valve and the cylinder are irrelevant unless one is trying to precisely calculate the pressure drops in that portion of the circuit. The simple, net result for regen extend speed is just the pump flow acting over the rod area.

Here's another data sheet on the same valve which indicates speeds and forces obtained with a 4" bore, 2" rod cylinder. You'll notice that the speed increase is 4 times, the same as the piston to rod area ratio. Also the force is reduced to 1/4, the same as as the rod to piston area ratio. There's no such thing as a free lunch and the significant reduction in force is the price one pays for the increased speed.

Prince LSR Rapid Extend Logsplitter Valve - Cylinder Services

I see the valve work ports are 3/4 and the in/out ports are 1/2. That's just the opposite of the typical control valve of similar capacity w/o a regen function. That makes sense because of the greater flow rates between the valve and cylinder during regen. In order to keep pressure drops and waste heat minimized, one should run 3/4 lines between the valve and the cylinder, even though the cylinder itself may have 1/2 or even smaller ports.

Rod