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Thread: Hydraulic return line
01-30-2013, 11:11 AM #1
Hydraulic return line
I'm finishing up a logsplitter project from years ago and need to address the plumbing: specifically the return from the operating valve (thru the filter) and into the tank. The filter assembly (a spin on 1 qt type with bypass) is threaded directly onto the 3/4"Xclose nipple that returns to the tank. Operating pressure of the system is 3000 psi, but I know the return side is negligible (or the filter would fail), but just how negligible? I want to use 3/4" SS braided hose with AN12 ends but could go ahead and use high pressure hydraulic hose and fittings if need be. The braided hose is rated for oils and fuels, but I dont want to lose 6 gallons of hyd oil with a hose failure. Anyone have real practical experience with this stuff. It's mostly used for marine and racing applications for fuel and oil lines. Pump output is 16gpm but return from cylinder could exceed that. I remember years ago mounting a twin element filter too far away from a tank and it failing big time due to pressure in the downstream return. Comments??
01-30-2013, 11:25 AM #2
01-30-2013, 11:30 AM #3
As long as your filter is rated for the flow your talking about you'll be okay but might want to do this. When i built mine I used high pressure hose just for the ease of the bends and layout. Then when I got to the filter I stepped up the size as large as I could with pipe. Pipe is fine on the low pressure side IF it doesn't rsetrict. I'm running a bypass and an additional 2 sppol with an autocycle valve. Pump is 28 GPM and all is fine.
01-30-2013, 11:56 AM #4
I would just get a real hyd hose instead of a made-up hose (Earl's?) with the bling aeroquip style fittings. Surplus Center has them for not much $ in pre-built lengths. If anything a crimped hyd hose is 100x stronger than a braided ss auto-racing-style hose if you happen to catch it unexpectedly.
01-30-2013, 11:59 AM #5
Tractor Supply will make up hoses to fit while you wait.
01-30-2013, 12:03 PM #6
If all is right your return should not exceed 30 PSI.
A note of caution, I have seen galv pipe shed flakes...don't use it on the outlet side of the filter.
01-30-2013, 12:57 PM #7
01-30-2013, 01:07 PM #8
Try to avoid the use of close nipples if possible. Close nipples have very little or no portion remaining that is the original/full pipe wall thickness. Pipe threads are sharp vee, so are are stress risers. On equipment prone to vibration, shock loads (as when a hydraulic spool valve goes closed), or bending/side loads (as from hoses), it is a good idea to try to avoid close nipples. If you MUST use a close nipple, try to get a Schedule 80 close nipple. Sch 80 is known as "extra strong" pipe and will have twice the wall thickness. Less likely to fail. McMaster may have the sch 80 nipples, or a good industrial/process piping supply house will.
Regular hydraulic hose such as Aeroquip or Eastman or Parker will have a woven steel wire braid reinforcement between the inner liner of the hose and the outer jacket. Regular hydraulic hose made up with swedged ends is going to be more than adequate for the type of hydraulic oil and pressure and temperature conditions on a wood splitter. No sense going for the SS braid/PTFE lined hose, it is an added expense. Other than resistance to UV and weathering, there is no real reason to go to the stainless braid/PTFE lined hose. You are not building a show bike, nor is this for something on aircraft. Regular hydraulic hose is used in many millions of applications on heavy equipment in severe service conditions without incident, and operates reliably for years and probably millions of cycles.
01-30-2013, 01:13 PM #9
01-30-2013, 01:30 PM #10
01-30-2013, 01:33 PM #11
You have a double acting hydraulic cylinder and the pressure is highest when you're extending the cylinder and splitting the log. The oil on the return side is flowing back through the spool valve and filter to the reservoir with little restriction or pressure on extension and on retraction, minimal pressure unless a piece of wood got jammed someplace then a build up of pressure and also if the seal let go in the cylinder..... wouldn't you get a spike of pressure on the return side? Just speculating but I would always run the good hydraulic pressure hose in that situation.
01-30-2013, 02:04 PM #12
Schedule 40 (standard weight) pipe close nipples are BAD NEWS, whether you have a low pressure or a high pressure fluid flowing thru them. They simply do not have much wall thickness left, and are almost a continuous stress riser due to the sharp vee pipe threads. On powerplant, process, and any kind of screwed piping, I was taught to avoid the use of close nipples, even on low pressure service. Where there is vibration, hydraulic shock, and side load, a close nipple will often fail due to bending fatigue, not due to internal fluid pressure. A schedule 80 pipe nipple is cheap insurance. I've seen schedule 40 close nipples fail by cracking at the root of the threads, on low pressure lines. A combination of vibration and side load produced bending fatigue.
Generally, when piping up a return line from a hydraulic valve back to the reservoir, a lower pressure rated hose can be used as long as it does not offer any flow restrictions. However, if the plan is to locate a mounting for a spin-on type filter in that return oil line, it will put the pipe connection in bending. While the load of the filter and mounting is negligible, the vibration in a wood splitter from the engine, pump pulsations, and from the hoses is what must be addressed. This is why I'd use schedule 80 nipples to connect a return filter mount.
01-30-2013, 05:43 PM #13
Now that I have seen some of your Logsplitters let me elaborate: Mine is painted black and I'm using SS fasteners and trying to use SS plumbing which will add to the cost, I know, but it looks good. I can get a 3/4" return hose made up with the SS braided hose and black (anodized) fittings for a whole lot less than a 3/4" high pressure return line in 3/4" size with SS fittings. I intend to use a 3/4" suction hose made out of the same stuff. Again, though, I don't want 6 gallons of oil all over the place!
01-30-2013, 08:03 PM #14
I can understand your wanting to use stainless steel. It is misleading as it is NOT as strong as carbon steel for bolting. It also has the nasty propensity to gall (cold weld) when stainless nuts are run onto stainless bolts, or stainless male pipe threads are screwed hard into stainless fittings. This is well known and something industry has dealt with for ages. Whenever possible, if we have to use a stainless bolt (as we do on certain application on hydroelectric turbines), we use a stainless stud or bolt and a Silicon Bronze hex nut. The Si Bronze is every bit as strong as the stainless, and being dis-similar, will never gall. And, it is galvanically inert or close to it, so that is not an issue. We NEVER screw stainless pipe fittings together dry. We always use some sort of pipe dope. Teflon tape is bad news around hydraulics as shreds of it have a way of migrating into hydraulic systems and winding up inside control valves and similar. We use paste-type pipe dope, carefully applied. Pipe threads are a sharp vee, and are known as "dry seal threads". They are cut on a taper and "wedge" and the sharp vee assures very nearly full flank contact on the threads. This close fit and "wringing together" is a recipe for galling with stainless steel on stainless steel. Pipe joint compounds are as much a lubricant or anti-seizing agent as they are a sealant. In theory, the pipe threads should make up to seal without any help from paste type sealants or Teflon tapes. We use "Swagelok" ferrule style tube fittings quite a lot in powerplant work, including for hydraulics. In stainless, they are quite pricey. Swagelok uses slightly different alloys of stainless (like 304 vs 316) for the gland nuts and fittings. Since a ferrule is used for the actual seal, Swagelok uses a slightly looser fit on the gland nut threads of their fittings. Otherwise, they would gall. I've made the mistake of "dry fitting" stainless pipe fittings and nipples together to try a fitup, no pipe dope or lubricant. Hand tight, the fittings galled and that was all she wrote. We got things apart with heavy wrenches, but the damage was done to the threads.
As for bolting in structural applications, I would NOT use stainless bolts. It may look pretty and not corrode, but you are running them in carbon steel frame and similar. I'd use grade 8 or A-325 structural bolting, made up with an anti-seizing paste on the threads and faces of the nut and bolt head and call it done. The stainless bolts are not up to the job of holding something like a splitter wedge or ram guide shoe together. No need to spend the extra money on stainless. IMO as an oldtime engineer, it is the wrong material for the application. It may not rust, but more importantly, it may not withstand the stress cycles and loads that carbon steel bolting would in your application.
If you use stainless pipe, it does not gain you anything over carbon steel other than corrosion resistance. The issues with close nipples and thin wall and stress risers are still there. If you use stainless steel screwed close nipples, go for Schedule 80. Same problems with breakage across the threads in applications where side-loads, stress cycling and vibration exist.
Most logsplitters I have seen (and one I built for friends years ago) were meant to do work, not look like they were spit shined for a show. Most are built of carbon steel, often as scrap of whatever people can make off with from jobsites. If they get a coat of Rustoleum gloss black or red, it is a step up. However, in terms of structural strength and mechanical design, they are right up there. A-325 structural bolting, welding done with stick using E 7018 by people who have generally welded in the power plants or building trades... piping run using 300 lb Black Malleable Iron fittings (this 300 psi is a steam rating, cold fluid rating is much greater) or screwed 3000 lb forged steel fittings and sch 80 nipples.
Stainless steel has its place, but quite honestly, it is not the best application to put it on a wood splitter. It is not overkill as it is not equal to sch 80 carbon steel pipe or carbon steel structural bolting. I would NEVER use stainless bolting on the splitter's axle mounting or trailer tongue if you plan to tow the splitter on the public roads.
By way of example: about 40 years ago, I worked as a young engineer on the construction site of a nuke power plant. We had to dismantle some large check valves to flush through the piping. The bodies of those check valves were cast stainless steel, butt welded into heavy wall stainless piping. When we opened up the valves, I was surprised to see the internals of those check valves were bolted with carbon steel B 7 grade stud bolts and class 2H heavy carbon steel hex nuts. I remember asking an older engineer whom I considered my guru about it. He explained that stainless steels were not the wonder wagon that too many people hitched their stars to. He explained that the B7 bolting and nuts were used inside the valves as higher strength was needed, and they did not want to screw a stainless stud into a tapping in a stainless valve body and risk galling. It was then that I was made to think in depth as an engineer, and started to think in terms of "the big picture", looking beyond the major "attraction" of stainless steel (corrosion resistance).
A splitter is a piece of outdoor power equipment. It sits outdoors, perhaps gets rained on, and issues with dissimilar metals (like aluminum parts bolted to bare carbon steel) might prove to have electrolytic action over time. But, a splitter is meant to be used. In short order, the paint gets worn off the beam, and there is wear and tear on it. You go out to split wood, and you may be working alone, heaving hefty log butts into the splitter. A splitter gets used and takes a bit of a beating where I come from. People use old hydraulic cylinders from junked heavy equipment (typically yellow), old structural steel for the beam and ram guide shoe (black), and beer kegs for the hydraulic fluid sumps, or they put an old beer tap handle on the valve for ornamentation if they are going out to build a show-grade splitter. The engines are usually having the paint burned off the mufflers and are grungy before too long. I've never seen a wood splitter look new and bright and shiny for too long if it does any serious splitting. Build it to use it and build it to last. That, and how it holds together and splits wood are what counts. Looks are secondary. Who looks at a wood splitter for "looks" out in the woods ? We look at the size of the ram and the engine and pump and how it's built and remark as to approximate tonnage or how easy it is to load log butts onto. Your back will be the ultimate judge of how good a job you do of designing and building a splitter at day's end.
01-30-2013, 08:56 PM #15
the suction line of choice is a wire reinforced type,to keep it from collapsing.two wire braided hydraulic hose is overkill,but the fittings (pressed on) simplify things and are less prone to failure.
the most abused piece of outdoor power equipment is a rototiller,next is a wood splitter.
its better to plan ergonomics into the build rather than asthetics.
i have seen them painted nice with alloy wheels.
i think they look great all shiny and stuff,just not my cup of tea.
as far as selecting the fittings,be it JIC,ORB or NPT- install them according to manufacturers spec.
close nipples are widely used in hydraulic suction/return systems,but the hex nipples are easier to dis-assemble.
my day job involves maintaining this very kind of equipment,biggest troubles are bolts falling out,battery and tank mounts breaking and ignition switch failure.
oil falling out usually filter vibrates loose.
01-31-2013, 07:55 AM #16
Whilst its true stainless bolts are weaker and there is the gauling issue to consider, you can easily get around it by just going to a larger sized bolt or more bolts for a given fixing. The key thing is to be aware its weaker and design around it!
01-31-2013, 09:33 AM #17
Standard stainless is rated at grade 2 (70,000 PSI) You can get around it by using 17-4 stainless (preciptiation hardening stainless steel) as it is basically grade 8 (170,000 + PSI). They are pricey though as a 1/2" X 1" will be over $10.00 EACH. I work a lot with the stuff and the hardened ones gall quicker than the grade 2. You SHOULD use antisieze on any of them.
There does come a point where the hardened stuff is a Minus a opposed to a plus from the brittleness of it but that's a whole 'nother can of worms. Growing up a friend made a splitter with a 8 inch cylinder. He ran it off an excavator as it took so many GPM to make it move reasonably fast. He had the back mount of the cylinder bolted and it would shut them out like bullets when shearing through a crotch sometimes. I Never saw anything stop that one other than breakage. Running a splitter with that much motor/machine was not cost effective either.