PDA

View Full Version : How do I build a Hydraulic Cylinder?



audrey
11-23-2002, 05:53 PM
I need Help, Advice on how to build Hydraulic Cylinders. I do not plan on buying one. I need to make them up special for one of my Projects. I will purchase the Tubeing and Chromed Shafting for them. Where do you get all the other stuff seals locking clips ect?? Also what type of clearances and or special fits do I need to adhere to? Any help would be appreciated Thanx Audrey

rbregn
11-23-2002, 06:30 PM
Look in the phonebook under hydraulics tell them the size and style of seals you want. If your not sure what kind, tell them your application, they'll help you out. Orings with backup rings will most likely do the trick for you. You'll also want a wiper for the rod ( basicly a seal to keep the dirt out of the seal) ask for a "can" style. As for clearances. Depending on the size of the cylinder, I would use .003" to .005" for the saft clearance in the end gland and .005 to .008" on the piston. You want to make sure when you cut the grooves for the orings, you don't cut to deep. Say you have a 3.000" ID cylinder with a oring with a .250" cross section. You want the minor Dia of your groove on your piston 2.500" http://bbs.homeshopmachinist.net//smile.gif
Rob

bspooh
11-23-2002, 06:49 PM
There are actually a lot of factors to determine when doing hydraulics...You need to know what pressures that you are working with...low pressures means that you can have a little greater clearance between piston and cylinder...high pressures mean that the clearance between piston and cylinders should not exceed about .003 maximum...I do high and low pressure cylinders daily..

If you are going to use an O-ring, then you must use a backup ring as well..back up rings are only used because they serve as "anti-extrusion devices"...but orings will have a lot of friction...if you don't want the friction then you must go with a poypak seal...if you need even more less friction then you need to go with a teflon seal..but warning, teflon seals will creep over time, and you will need to replace these seals more often..

Is your hydraulic cylinder a single action, or a doulble action...this is very important...you cant' just measure the cross sectional thickness of an oring and then make your groove in your piston accordingly...orings must have a pre set tension on them or else they will leak under very low pressures...they have books that will tell you what your bore should be and your groove diameter as well as thickness and tolerances...

Remember when doing bores on hydraulic cylinders, your finishes should be no better than a 16 RMS, and no worse than a 32 RMS...do not try and get a mirror like finish..this is bad because of the increase in friction...if you have too fine of a finish, then you need to hone the cylinder out just enough to get a cross patch pattern...imagine sliding rubber over a mirror...doesn't work too good does it?? keep your finishes right around 16-20 RMS....

Brent

crypto
11-29-2002, 01:22 PM
Brent, Rob,

I found your information helpful. I have the Parker o-ring tech books but had forgotten about backup rings. I want to convert a hand operated grease gun into an oil pumping gun to lubricate my bridgeports. Do you have any suggestions? McMasters sells them for $124, too much for this miserly one.

Oscar

[This message has been edited by crypto (edited 11-29-2002).]

Mcostello
11-29-2002, 09:11 PM
If you would like I will tear down the little pistol type grease gun that I converted to heavy waylube. Just got O ring at store, made groove .010-.015 smaller on O.D.( I think) Same width. Doesn't leak will move with suction of pump applied. Took out spring, yeah I know - cheating. Works great.

crypto
11-29-2002, 11:10 PM
Costello,

I hadn't thought of using one of the small pistol type of grease guns. I had intended to cut down the length of one of the full sized grease guns but if the little one works for you then that is what I shall do.

The previous users of my mill had pumped it full of auto grease and it gets rather stiff to move. My old one, the round ram mill, has grease in it but it needs the grease to take up the slack and keep it on the straight and narrow path.

Thank you.

Oscar Ortiz

audrey
12-03-2002, 07:36 PM
<font face="Verdana, Arial" size="2">Originally posted by bspooh:
There are actually a lot of factors to determine when doing hydraulics...You need to know what pressures that you are working with...low pressures means that you can have a little greater clearance between piston and cylinder...high pressures mean that the clearance between piston and cylinders should not exceed about .003 maximum...I do high and low pressure cylinders daily..

If you are going to use an O-ring, then you must use a backup ring as well..back up rings are only used because they serve as "anti-extrusion devices"...but orings will have a lot of friction...if you don't want the friction then you must go with a poypak seal...if you need even more less friction then you need to go with a teflon seal..but warning, teflon seals will creep over time, and you will need to replace these seals more often..

Is your hydraulic cylinder a single action, or a doulble action...this is very important...you cant' just measure the cross sectional thickness of an oring and then make your groove in your piston accordingly...orings must have a pre set tension on them or else they will leak under very low pressures...they have books that will tell you what your bore should be and your groove diameter as well as thickness and tolerances...

Remember when doing bores on hydraulic cylinders, your finishes should be no better than a 16 RMS, and no worse than a 32 RMS...do not try and get a mirror like finish..this is bad because of the increase in friction...if you have too fine of a finish, then you need to hone the cylinder out just enough to get a cross patch pattern...imagine sliding rubber over a mirror...doesn't work too good does it?? keep your finishes right around 16-20 RMS....

Brent</font>
Thats really nice guys but How do I build Hydraulic Cylinders?
I allready have the plans for the Grease Gun Modifications required for the Gun to supply high pressure oil.
I purchased this Information from Guy Lautard Many Years ago.
Thanx Audrey

rbregn
12-03-2002, 11:02 PM
Find one at a scrap yard or a local shop that works on them and use it as a sample. Basicly it is a tube with a shaft coming out of one end with some kind of eye on each end. the shaft has a piston with seals on it to keep the oil on the same side as it came in. There is also a seal around the shaft where it comes out of the end gland. which can be screwed on to the tube. You can use snap rings to hold the end cap on, but I find when you have to take these apart you will cut your seals in the snap ring groove.
Hope this helps!
What is your general diamensions and application? Maybe I could get more specific.
Rob http://bbs.homeshopmachinist.net//smile.gif

docsteve66
12-04-2002, 09:47 AM
audrey: There are a lot of factors involved. Be a lot easier to assist if you gave some info. How much load do you have move? Must the cylinder be single acting or doulbe acting, what pump pressures do you intend to use? How often will it be used? what will happen if the cylinder fails in use?

Questions of this sort are the reason we (I at least) want to know the final application- knowing the application tempers the replies, and leads to asking simpler questions. For a low pressure system, pvc may work. For a single acting ram the seals around the rod are of little importance, just need a guide. The mountings are important because the rod needs to not buckle against the guides. I see lots of commercial equipment where the basics are ignored- and they last until the warrenty runs out. Older back hoes are especially poorly designed but still operate for years but maintneance is high.

Come lady, give us a chance!!!!! http://bbs.homeshopmachinist.net//smile.gif
Steve

halfnut
12-04-2002, 10:22 AM
Audrey,

Many ways to build a hydralic cylinder, kinda like killing a cat. Don't say I said that to my furry friends they might get offended, but you get my drift.

Cheapest most common type is the tie rod cylinders, gland end and mount end sanwiching the tube with rods holding things together.

Reverse engineering is what you need to do. Disect some dead cylinders and see how they are made, I've seen many variations on these simple devices.

As it has been said a hydralic shop can supply you with seals and such, also our farm supply stores carry kits for common AG cylinders such as Prince. These kits come with o-rings, backup rings and the wiper seal, buy a kit for the bore size and the shaft size. Cheap way out, but these are for O-ring piston cylinders which are on the bottom as far as longevity goes.

Better cylinders have better types of seals, used to be that the chevron type packings were the best, nowdays there are some nifty designs. Polypacks are the most common of the better packings. Used to work on German made forklifts, they used some seals that were most unusual, thin sealing ring with notches supported by a large O-ring.

Cylinders which always amazed me were the ones used on Doall loaders, had seal rings which appeared to be cut out of side walls of old tires. Crude but they worked well.

Look at some old cylinders.

docsteve66
12-04-2002, 11:38 AM
Audrey, Look at northern hydralics catalogs. The low end "prince cylinders" seem to hold up well. I can not buy the materials for what they charge for the complete cylinder. For a cheap- real cheap- single acting cylinder, I have used pvc pipe. two pieces telescope together and a brake (automobile) cup for the piston worked well. I have also spent weeks getting a 13' grinder to hold less than .001 inches on the ram rod for a aircraft noce gear strut. You decides what you want, the risks involved and put it togehter. some big equipment leaks down at a fairly fast rate because the cylinder is so rough. The chevron seals are probably the most rugged, forgiving seals for both the rod and piston,
but you need to disassemble a cylinder of the sort you need to see how they did it in at least one case. larger cylinders have a lot of friction. Probably you can't collapse them without pressure or rigging a lever.
and beware of using air to operate them. Once they start to move, they WILL go to the end of their travel even if you or a wall are trying to stop them. Air is good for testing but for petes sake be sure the piston can not come out and hurt you. Even the blast of air that follows the piston will sting bad if you are near. and oils sprays around (eyes and skin).
So much depends on what you expect from your cylinder and how long.

docsteve66
12-04-2002, 09:15 PM
Called a friend who rebuilds hyd cylinders. He suggests going to some place that repairs cylinders. You buy an old cylinder with damaged bore, but good rod. He says replacement tubes are cheap or even buy a long cylinder and cut out the bad spot.

He cuts the bottoms off, the tops off. machines the bottom with a shoulder and welds in place. Some tops screw in the tube. he says its faster to weld a new top on,than to cut threads. just make a v and square cuts. He has a large jig to hold every thing square. basicly a lathe with no motor. He advises to not try to machine the glands, salvage or buy. mountings? if its a new job, try to keep the tube mounted so it will not buckle. use as long as tube as you can, testrict the stroke with a pipe so it will not "hyper " extend and buckle.
A good inside finish in not needed for double acting rams. they leak but the operator (on construction equipment) only notices it when traveling. the rest of the time they are "playing the controls" anyway.
Single action rams need a weep hole to prevent hydraulic lock up when the piston leaks (which it will sooner or later).

we were discussing small rams (4" id). If yu want info on calculating lifting power, you gotta know working pressures. The force is greater than the retracting force by the area of the rod.

Thats about all i found out.
Steve