What size hose to use for 28 gpm?

4570Man · Jun 28, 2017

It's a wood splitter

LD1 · Jun 28, 2017

Just did some calculating to expand on what I posted earlier.

If your 5" cylinder has a 2" rod, while retracting and pumping 28gpm into the rod port, 33gpm needs to flow out the base port.

If this 5" cylinder has a 2.5" rod, the base port low increases to 37GPM.

SO keep those in mind as well when selecting valve size.

An ideal splitter will have a LARGE rod. (but cost is usually prohibitive.) Because a large rod makes for a quick return stroke which is a wasted stoke anyway. But the larger the rod gets in relation to the bore(faster return), means you have to expen fluid that much faster out the base port.

So lets say someone in your shoes decides on a 5" cylinder with 2.5" rod and 28gpm pump. Shopping for valves, decides on a 25gpm valve because....eh its close to the 28gpm rating of the pump, and the next jump adds alot of cost. But not realizing that the valve is grossly undersized for the return flow on the retract stroke, and a 40gpm valve is needed.

There is another solution to that though, if the smaller valve is chosen, and you usually see it on some custom splitters that guys are building for speed. That would be a dump valve. It has a one way check valve basically, and 3 ports. Its plumbed inline with the high pressure hose going to the base end of the cylinder (extend function) and the third port on it gets plumbed back to tank.

Under normal operation when extending, the fluid flows from the valve to the cylinder and check valve port to tank is closed. Under retract stroke, one way check valve opens (fluid flowing the opposite direction), and now the fluid has TWO paths back to tank. 1. Through the return valve, and 2. through the valve

muddstopper · Jul 3, 2017

What do you do when you wake up in the morning at 4am. You get on TBN and respond to old threads.
I am guessing that since the OP is building a wood splitter and wanting to use a 28gpm of oil, he is using a two stage wood splitter pump. Since the pump size is 28gpm, I am guessing the 5in cyl LD1 used in his example, is probably correct. OP could have given a little more info in his fist post. Anyways, I have a similar setup, 5in bore cyl, 28gpm 2stage pump. I do use 3/4 hoses and a 25gpm control valve. I need a dump valve, but havnt gotten around to it. My hyd does get hot, but I seldom run wot with the engine and havnt had any serious issues. I slapped my machine together using parts on hand, even used used hoses. Started out with a 14gpm vane pump and a 4in bore cyl. Then bought the 5in cyl from northerntool when it was on sale. Then needed the bigger pump to make up for the speed lost going from 4in to 5in. If I was going to split a lot of wood, every day, I would get the dump valve, but as it is, I seldom run my splitter more than 45min to an hr at a time. I have a 6way wedge, so 45min of splitting is a big stack of wood. My rest breaks and stacking time give my machine time to cool off.

After all this rambling, some things to look out for. First check out your cyl ports, just because a 3/4in fitting will screw into it, doesnt mean the hole inside the port is 3/4in. The northern tool 5in cyl has about a 3/8 dia hole inside the fitting boss. Looks to me that they drilled the barrel and simply welded the large fitting over the hole. It gets worse, I took my new cyl apart to drill out the hole and found the new cyl full of metal shavings. If I had simply screwed in the fitting and used as it came from the store, I would have trashed the rest of my hyd system.

Second thing to look out for is hyd tank size. Wood splitters are notorious for small tanks, I suspect my 10gal tank is one reason my machine heats up, oil just doesnt have time to cool off before it is pushed back thru the system.

Third. I havent seen a standard wood splitting valve that is rated for more than 25gpm. I guess the first commercial box store splitters used small pumps and the industry just sort of stayed stuck in a rut producing parts. Anyways, consider the dump valve, this will reduce heat build up and give a slight increase in speed.

Fourth, A 5in bore cyl produces a lot of force, whatever you plan to use for a beam, if it aint strong, your going to bend it. My hbeam is a 6x6. 1/2in thick. I plated the top with 1/2in plate, makeing it 1in thick. I plated the sides with 3/4 plate, both sides. I havent bent it, but I sure have made it bow a time or two.My wedge is adjustable and will go up to 24in tall. Make it a 6way and you have created a lot of leverage on the end of a light duty beam. Build it right the first time, overbuild it if possible. When you think you have over built it, brace it some more. You dont want to bend it and wish you had made it stronger.

Suns coming up, time to go fishing

4570Man · Jul 3, 2017

I think the hole into my cylinder is about a 1/2".

muddstopper · Jul 3, 2017

You will want to drill that out if you can. Whole point of using a 28gpm pump is to speed things up and that 1/2in hole aint helping. There are several different ways to fix the hole problem, depending on the design. Some folks simply plug the exsisting ports and drill and weld new ones on. Mine, I just ran the largest drill that would fit the port and drilled it out, but my port size was already 3/4in. Either way, plan on pulling the piston before drilling to make sure you get all the drillings out.

4570Man · Jul 5, 2017

Too late now. I welded the pins in so I can't take the cylinder apart to clean out the metal cuttings. Even if I don't get optimal cycle times it won't be the end of the world. I've currently got it on aux ports that are probably 10-15 GPM for a test run and the cycle time isn't that bad.