hello, my predicament it seems is not uncommon. i purchased hydraulic thumb to install onto my JCB JS240. welded it on, plumbed hydraulics and surprise surprise, the thumb only worked one way. i was told it appeared i had a mono direction hammer circuit running and to convert to bi directional would cost me $4500! of course i have spent a small fortune on the thumb, the welding, and the hydraulic plumbing so another $4500 seems to be overcapitalisation and i am thus looking for alternatives. i have been researching as much as i can about this problem and it seems i have a couple of options. 1)Tee off the bucket ram to make thumb and bucket act like a clamshell. 2)use a bi directional solenoid to switch flow back and forth. both options will still cost me a minimum of $500 i suspect, but i thought about a new idea this morning and would like the opinion of those who have experience in these matters. is it possible to make the pressure relief on the thumb much lower than the bucket so that when i want the thumb to retract i can force it back with the bucket? Most of the time however the thumb can be used like a mechanical thumb and stay in the most desirable spot. The only time i would early need to retract is when switching to bucket operations with no need for the thumb. there should still be ample pressure in the cylinder to keep it stable while handling objects, but when finished with thumb force back to the stick with bucket. is this a feasible alternative? thank you for any help you can offer.
Antpoo, welcome to HEF! Your best bet is to add a solenoid switch on the dipper (verify that your machine does not have a double acting circuit before spending any money- if it does, there should be a selector valve to switch between hammer and double acting functions). A dual crossover relief valve will allow you to set the pressure lower on the thumb (cost should be under $100) for a 3/8"bsp valve with 40l/min flow)
Good day Antpoo You have a host of options avilible for your aplication, dual acting option spools are in general controlled by a pedal valve, these pedals used are in most case's the same as the crawler control ( Kawasaki). If you have a breakers yard or used spare source you can obtain these cheaply. Plumbing is not difficult if you need detailed information just request it from excatech.com. If you need more help just follow the link there is no cost in good advice. Kind regards Uffex
You said that it " appears" that you have a mono directional circuit. Are you positive about this it seems to me that if the operating lever was set up to work in two directions such as a rocker pedal and not just a single direction push that the valve should have the option. if you visually chase the return line from this circuit does it simply return to tank. Cat has a quarter turn valve tucked down in there that changes it from mono to bidirectional. I would want to be positive about this before anything else. That being said. I think you could use an electric solenoid to reverse the direction of flow through the thumb. I have a Cat 311 that has a Wain Roy Wrist attachment. We installed an electric solenoid operated by and old style headlight dimmer switch mounted on the floor. You can switch functions instantly all day long. This may be an option. to look at.
Welcome to HEF Antpoo. :drinkup I'm not familiar with the JCB JS240, but I'd be really surprise if a machine that size only had a single acting auxiliary circuit. It may be hard plumbed for single acting only and require some changes in plumbing. Could you possibly follow the lines that gives the thumb pressure back to the valve that controls it and take a picture of the valve? If you could post a picture we might be able to tell what you have.
Thank you for replies. I said appears yes because we are not certain. The hammer pipe goes up the right side of stick and dipper to a large tap at the end. We have plumbed a hose from this large tap to the hydraulic cylinder, which also has the return hose attached and returns oil to another large tap on the left side of dipper arm and stick. It returns to a filter and from the filter it goes to tank I believe but I cannot be certain as it was hard to see amongst the maze of hoses. The circuit is controlled by a foot pedal on the right hand side of the track controls. The foot pedal rocks both ways and has two pilot hoses connected to it from underneath. I need excavator for my demolition job today so I was trying to find a quick solution as the hydraulic professionals have been very tardy in replying to my requests to take on the job, perhaps they are too busy. Anyway I thought that retracting the thumb was not really that important anyway and that as long as it went forward toward bucket into a position much like a mechanical thumb, I could just use bucket to retract it all the way back when I don't need it without having to get out of cab. Would this put too much stress on the system or the cylinder? Can the relief pressure on the circuit be set so as the oil will return from thumb to tank easily and not damage thumb ram? The thumb cylinder itself does not have pressure relief however.
I will take some photos today and share. Thanks again
Ps, I should also mention the engine bogs down and labours heavily if I use the rocker pedal in reverse so at least that says the option is indeed there, but that it is blocked somewhere.
Hi willie, The JCB consultant over the phone said that it was these changes in plumbing that were going to cost $4500. This is AUD by the way (very expensive here in OZ). I was in disbelief and told him this is just unacceptable, especially when others tell me it is a day job only. I too could not believe a 2005 machine would have a mono circuit without a tap of some kind to switch to bi direction.
Ok I have had a hydraulic guy come out and view and offer a quote of $850 to plumb a hose to make the thumb retract. Apparently the lines from pedal are connected and it is a simple job that should only take a few hours. But if so, doesn't $850 seem a little high?
G'day Mate those blokes are on $90 plus an hour, add in some hose and fittings and could easily be 850. Are you sure these no switch in the cab to go from say bucket mode to nibbler or hammer mode? Cheers