JD 70A lift speed issue

[J_J]

The load is providing pressure.

With a good valve, and with bad cyl seals, with a load pulling on the rod, where is the fluid going except to the other side of the piston. That is the reason that the lift arms drop and bucket curls down. If the seals were good, the cyl rod would never move in a locked situation.

 

[dfkrug]

The load is providing pressure.

With a good valve, and with bad cyl seals, with a load pulling on the rod, where is the fluid going except to the other side of the piston. That is the reason that the lift arms drop and bucket curls down. If the seals were good, the cyl rod would never move in a locked situation.

MECHANOS' problem is with the FEL boom. He reports that is does not
go up very fast, but it stays up when the joystick is released. So the
load (boom) is pushing on the boom cylinders, not pulling. In other
situations where the load is PULLING on the rod, movement is possible
if the fluid cavitates with the valve closed (and bad piston seals).

 

[Mechanos]

Well, my seal kits are in, but I haven't had a chance to touch the tractor is days. Had to work 7:30am-10:00pm on Fri. 9:00am Sat to 5:00am Sun., then 9:00am Sun. to 6:00pm Sun.

 

[J_J]

I was playing with some cycle times for a single 2 in cyl with 1 in shaft, and a 24 in stroke.

At 5 GPM, the extend speed is 6.1 in per sec, so time to extend would be 3.93 sec with a straight on push.

Retract speed would be 2.92 sec.

Mechanical hook up will change this based on the distance the push point is from the hinge base line. If the connection points closer together, time will approach straight on push. Since we are talking about filling up two cyl, the time will be even slower.

I would suspect those cycle times you posted unless the characteristics of the cyl and the GPM are different.

 

[Mechanos]

The cycle time of the cylinder would be indepent of the connection point geometery. The volume of the cylinder isn't changing. Now the angular velocity of the end of the boom or whatever would certainly change depending on the geometery.

Anyway, my boom cylinders are 1.5" with what measures to be close to a 1 3/8" rod (not quite... but it is bigger than 1.25"). I don't think total stroke is 24".... something less than that.

Also, I was just looking back through the specs in the loader manual and I see that they based there numbers on 7.2 GPM. The pinhead that calculated those specs probably didn't account for the 30% of total flow going to the power steering circuit.

EDIT: I screwed up my measurement... it's about 1 1/8th rod diameter.

I was playing with some cycle times for a single 2 in cyl with 1 in shaft, and a 24 in stroke.

At 5 GPM, the extend speed is 6.1 in per sec, so time to extend would be 3.93 sec with a straight on push.

Retract speed would be 2.92 sec.

Mechanical hook up will change this based on the distance the push point is from the hinge base line. If the connection points closer together, time will approach straight on push. Since we are talking about filling up two cyl, the time will be even slower.

I would suspect those cycle times you posted unless the characteristics of the cyl and the GPM are different.

 

[dfkrug]

I would suspect those cycle times you posted unless the characteristics of the cyl and the GPM are different.

When a piston seal gradually leaks more-and-more, the lift time (cyl extend
time) will get slower and slower, yes?

Mine got so bad that at 70F or so, the FEL would only rise about 1/2-2/3.
20 degrees cooler and the cooler oil allowed full-height lift, tho slow.

Above I mentioned cavitation in a rod-pull situation (as in bkt dumping), but I
suspect that sucking air into the cyl past the gland seals is much more
common. That is my suspicion; I did not run any experiments.

 

[Mechanos]

Just noticed something interesting tonight.... my loader has 3/8" hard lines and 3/8" hose that connect to the male tips of the quick disconnect with SAE-6 ORB fittings. The female half connects to 3/8" hard lines also with SAE-6 ORB fittings. What's so interesting about that? The quick couplers are 1/4" sized Parker 4000 series. I cannot find those fitting anywhere in the aftermarket with -6 ORB connections... so, I guess it's a JD "custom" thing. But what I find interesting is that every listing I can find for 1/4" 4000 series connectors specs them at 3 GPM. My tractor specs 5 GPM to the SCV/Rockshaft circuit.

 

[dfkrug]

The quick couplers are 1/4" sized Parker 4000 series.

Are you sure those are not 3/8 (-6) QD fittings? I don't have a 955 here
presently, but I don't recall that they were that small. It is true that
DHH does not carry QDs with ORB-F connections.....I think they only have
NPT connections. You may find them at other places, however.

As for the flow restriction, note the the 70A loader comes with orifice-
style restrictors at the cyls.

 

[Mechanos]

Are you sure those are not 3/8 (-6) QD fittings? I don't have a 955 here
presently, but I don't recall that they were that small. It is true that
DHH does not carry QDs with ORB-F connections.....I think they only have
NPT connections. You may find them at other places, however.

As for the flow restriction, note the the 70A loader comes with orifice-
style restrictors at the cyls.

Yeah. I had a bag of 1/4" male tips I bought to replace some of the fittings on my attachements for my 322 gardent tractor. I used one of them to attach a pressure gauge to my 955 measure the relief pressure on one of the SCV ports.

I replaced the seals in the boom cylinders tonight. One was an unholy nightmare to get apart... the other one came apart like it was built yesterday. Anyway, the boom does raise a little bit faster, but not a lot. However, the boom raise relief pressure reading is now solid as a rock instead of bouncing all over the place like before.

As for the restrictors... the 70A manual states that the restrictors (if there are any) would be located between the 3/8" hoses and the hardlines where they connect on the boom. I checked all those locations, but I did not check at the cylinders.