2-stage pumps versus Pressure Sensitive Regenerative Valves

[AKKAMAAN]

from topic: HP requirement for 22gpm Pump?

+1 on that. yes it will be pricey on many levels, but it will give you power and speed and production. You decide how much that is worth. For me, time is worth a lot. The old saying from the hot rod days: 'speed costs, how fast can you afford to go?’

Ian, your feeble mind must be decent as you have figured out exactly where hydraulics has gone in the last decades: Running smaller pumps, at higher speeds, higher pressures to get the power in smaller components, lines, space, etc. etc. Farm tractors or bulldozers in the 1950's were 850 psi, with big fat cylinders to get the required forces. Now hydr excavators are 3500 to 5000 psi, and some applications push 6000 psi and above in open loop systems, not hydrostatics. Much of that is materials improvements, and much is fluid/additive improvements.

So you are correct in that a smaller pump at higher pressure can transfer the same power. (hp = flow times pressure, so increasing pressure decreases the required flow for the same power). In this case, more force at the wedge with smaller cylinder and valves and lines.

However...... the rub for a consumer is that 3000 psi is about the maximum for practical reasons. Maybe some 3400 psi per prior posts here. Common half inch two wires hoses, 37 degree flare fittings, cylinder metal tubes, cylinder cheap lip or o-ring seals, pumps, and spool valves are all generally designed about that maximum because that is where industry was for a long time. Since the largest market = largest quantity of production = lowest prices, that is the best consumer choice for the OEM splitter people. Much easier to add cylinder size than to get higher pressure components through the entire system.

Thus, assuming you are limited to about 3000 psi, this defines cylinder size for whatever force you want. Pick a speed and that defines flow and hp. Or, pick a hp and that defines maximum flows. Engineering is a game of tradeoffs, and every addition to force or speed costs money. The OEMs have settled into 5 hp, 8 hp, 12 hp because they are common engines and pumps are available. The pump people have settled into 11-13-16 gpm sizes because they match the engines well.

OK, back on topic. The 22 and 28 are in the larger frame, but both have the same small section, .465 cubic inches/revolution. (BTW, the 11 and 13 also have the same small section of .194 cir. That’s why I push the 13 gpm pump instead of the 11.) Add a large stage of .93 cir and you get 1.395 total cir for the 22 gpm version (at 3600 rpm). Add a large stage of 1.395 for total 1.86 cir and it is a 28 gpm version.

Thus, the low speed, high pressure performance and hp required will be almost the same with either version. For 2500 psi that is about 12 hp. For 3000 psi it is about 14 hp. So a 16 to 18 hp engine would be great. Larger engine, say 20 hp, does not give more psi or more speed, it just runs at slightly less then WOT to where it produces the required 12 or 14 hp. But it can do that when it is tired or out of tune and still have plenty to account for the slight extra power of the unloaded section.

Now, large section. Barnes shows performance charts for unloading settings of from 400 to 900 psi, with factory settings of 650. 900 psi is 13 hp for the 22 gpm, and 17 hp for the 28 gpm. I was emailing the Barnes AE a year back about increasing a 11 or 13 gpm pump up to about 1100 psi with shimming. It would not be blessed by Haldex at all, but was within the torque capabilities of the shaft. You could probably do it on a larger pump also, but realistically, the 900 psi matches the engine hp pretty well.

Next, do the cylinder calculations to match the flows. Maybe 28 is too much on retract speed. Remember 28 gpm into the rod side is 35 + gpm out the closed side, so the spool valve and return filter and lines all around get much bigger.

So, bottom line, if you go small engine I recommend 13 pump over the 11 pump. The next jump up is the 16 gpm. If you make the big jump in frame size and cost to the D series, you may as well go the 28 instead of the 22.

I would volunteer an excel spread sheet with all this on it but I am searching for it. Send me a pm with an email address. I can’t attach files to PM’s back. Might take a few days till I get to the old home computer.

kcj

Hi KevinJ
You really have this into a science...I read that whole thread today...50+ posts...
There are enough "pirates" out there today, I didn't want to steal the thread so I started a new one.....

I have zero hands on experience of 2-stage pumps.....and I still feel like I don't want to approach that path....

I can see these minuses and plusses....please argue if I'm wrong...
Minus:

• more expensive and vulnerable pump...right?

• whole system have to be flow dimensioned for pumps highflow capacity and pressure dimensioned for pumps high pressure capacity....some 4 wire hoses on higher capacity pumps huh....

• hard to find op valves rated for high flow pumps (short cycle)

• you will be "stuck" with the manufacturer settings on the pump

Plus:

• easy setup on standard, low to medium flow, "slow cycle" systems, where you don't care about that "extra"....like the inexpensive bulk splitters that are sold everywhere...

• ??

I have dealt with Pressure Sensitive Regenerative Valves, PSRV, a bit, and never had a problem with them...of course they are made to be a "pump helper" when gravity can retract the piston....but they will also do well as a "gear" unit on a logsplitter, actually I believe they are used on some of the firewood prcessors out there...These Sun PSRV's, diminishes the regeneration progressively so you can utilize maximum hp from the engine through the whole splitting stroke.....

Minus:

• one extra component to plumb into the system...

• 150-250$ expensive?? depends how you value that main features....

• I takes some "new sort of thinking" to optimize Bore And Rod Diameter,BARD, ratio, and pump size...

• ??

Plus:

• mentioned above..diminishes the regeneration progressively so you can utilize maximum hp from the engine through the whole splitting stroke.....in other words....it delivers variable flow, depending on splitting resistans (pressure), cycle as fast as possible on that rpm and hp from engine....

• you can get very short cycle times with a smaller pump, max piston speed dimensiond by the cylinder rod diameter

• you can get very high splitting force by choosing a large bore cylinder 5-6"+

• valves and plumbing can be dimensioned for the true pump flow/pressure, except for the part between the PSRV and the cylinder. No extra large directional valve needed for high speed (high flow) operation
• easy to rebuild single stage systems into very high productive splitters (if cylinder have a resonable BARD ratio)

Please, anyone, add some input to this.....

 

[triptester]

The main purpose of 2-stage pumps is to reduce overall cost. Single stage pumps require more horse power for max. flow.

Example, a 16 gpm 2-stage pump requires an 8 hp. engine, most of the time it is sending 16 gpm to the cylinder unless higher pressures are required when extending. Retraction will always be at 16 gpm's.

A 8 horse power engine will only operate a 4 gpm single stage at max. flow and pressure. So to match cycle times of a 2-stage pump a single stage pump will require more horse power to produce more gpm's or a more expensive regenerative valve plus more hoses The hose pressure rating required is determined by max. pressure not by pump style.


Here is a quote from the Prince literature "Laboratory testing has not shown a significant difference
in working cycle times between single stage/rapid extend
systems and two stage systems."

For a basic log splitter a 2-stage set up is the most cost effective. If manufacturers thought they could save a dollar and be able to claim any advantage with any other method they would jump on it.

 

[kevin j]

main purpose of 2-stage pumps is to reduce overall cost. Single stage pumps require more horse power for max. flow.


yes, lower overall costs for equal performance. the two stage pump costs more, but is much cheaper than the big engines required for an equal speed equal force single stage system.

-Backing up for a definition: Regenerative flow is when the return oil out of the rod side is connected to the oil going into the closed side on extend. In essence, the pump flow then is only pushing the area of the steel rod shaft. So 2 or 3 gpm from pump can rapidly extend effectively a 2 inch single acting cylinder. Only the force of the two inch rod diameter, but that is a limit of physics and horsepower. Then, at a certain pressure level, the regen valve sends rod side oil back to tank via the normal path and the pump connects to the full 4 or 5 inch bore area for lower speed and higher force.

-Two stage pump is simple and rugged, slightly more complex than single gear pump but just a check valve and a sliding spool unloading valve. Per with your background it will be piece of cake. Way less complicated than piston pumps, load sensing, etc.
-the regen valve Per refers to (many brands) does regen externally to the cylinder. They were often added close to a cylinder to speed it up without having larger lines and higher flows in all the piping from the pump.
-Biggest functional downside is that regen ONLY works in rod extend direction. So in the retract direction, the speed is still the slower single stage pump flow.
-Another downside, the speed can get really high if the rod diameter is small. a 4 B 2 Rod cylinder would be 4x the speed on regen. A 1.5 Rod would be 7 times the extend speed on regen, so things can get out of hand quickly. Math needs to be done to make sure it is a good match.
-Cost of the external regen valve and fittings will be more than the entire two stage pump. Not cost effective usually.


-The Prince regen 4th position built into the manual spool valve is a whole different story. Brilliant product for a very small market. The target is the really cheap machines with 2 or 3 gpm single stage pumps and 3 to 5 hp engines. There, the extra $75 for two stage vs one stage pump (plus larger lines, filter, strainer, etc) might make the splitter $125 more than an equivalent single stage circuit. Tough to build a tiny machine that doesn’t creep up in price too close to the larger ones. So they end up with single stage pump to keep cost down.
The cost of the regen position in the Prince valve is essentially zero. Slightly longer spool and travel of lever, an different grinding of the spool. There is no pressure or control circuit, it is manually moved by the human operator only. The cost comes more with the lower quantities built, vs the mass market detented valve which is made in large production runs.
So, for an extra $20 maybe, the tiny splitter can get much faster extend time than the single stage competitor.
I will bet the regen spool won’t take much market. It is a manual function, the operator needs to move the handle back and forth between positions. The cylinder needs a fairly large rod size to have a safe high speed. And the retract is still slow speed, small pump section. But for the intended niche is should be interesting to see the OEM’s reactions to it.



Trip: the Prince site was using that quote as a sale pitch to show that the regen valve was a good thing, to be used instead of a two stage. Not that the conclusion was the regen was not good. I think they tacitly agree, without stating, that the two stage is the best choice, but that the regen is a good cost effective way of doing almost the same thing. I agree with your statements, and especially the conclusion. If the larger splitter mfrs could save a buck and get same performance, they would do it. But the bigger rod and limited retract kills it on the bigger splitters. Two stage for sure.



Per: There were so many 'my log splitter don't work' posts at the HydrPneum board that someone who knew my background and hobbies with wood cutting (I think it was Bud T) suggested I come here and deal with the hydraulic questions here where the interest is more appropriate. It has been a blast for me, hopefully I have helped some. And I have learned so much on the saw site.... been expensive on that side though : )
I'd like to see you post some pics of the BIG wood handling stuff. Lots of droolers here over mechanization.

kcj

 

[ericjeeper]

Kevin

I am sure others as well as myself appreciate reading your writings. You know your ****.