Bobcat 853 - front auxiliary valve only works in one direction

[ags_virginia]

Hi, I recently purchased a Bobcat 853 (SN# 510126350) equipped with the Apitech front auxiliary control valve, but discovered that the valve only operates in one direction. Front auxiliary electronics are working fine, and both solenoids receive 12V power when function is triggered by the switches. I also ruled out the solenoid malfunction by swapping the solenoids. There is no audible change in engine / load when malfunction is observed, and so it seems the problem is with the valve body itself.

The service manual is silent with respect to "rebuilding" the Apitech valve, which is now obsolete. The parts diagram shows the solenoids (#27) and pilot orifice (#26) as separate parts, and also states that the replacement solenoids have an an orifice build-in and the separate orifice (#26) needs to be removed when replacing the solenoids. In my assembly, the orifice is built into the solenoid (tiny ruby orifice), so I imagine it was replaced at some point. I tried to see if maybe there was an old separate orifice left in the assembly which could be plugged, but nothing fell out of the solenoid port, and I could not pull anything out with a seal pick.

I am speculating that the following root causes could exist:

1. Pilot port delivering hydraulic fluid to the spool is obstructed
2. Spool rod is obstructed / has high resistance in one direction

My options as I see them, are:

1. Tear down existing valve, and attempt repair by cleaning / blowing all the passages with compressed air, and and replacing whatever seals I can still source from Bobcat, McMaster, etc.
2. Contact Parker (who purchased Apitech) and see if they have some alternative valves in the same form factor
3. Replace with a different directional valve (i.e. Eaton) that matches or exceeds specifications of the original Apitech

I am wondering if anyone else has observed a similar issue, or has recommendations on rebuilding these units in the absence of readily available parts. I will appreciate any advice on the matter.

 

[ags_virginia]

To add to the initial post above, below is the hydraulic diagram of the Apitech front auxiliary valve on a bobcat 853. It's a 4-way three position valve, with spring self-centering. I have hydraulic output on the male aux port, but not on the female. Also I see a steady stream of fluid coming out out of both solenoid ports when they are removed, which tells me the pilot input to the solenoids is not blocked. I am not sure how the various restrictions (#35) are created, but it seems the net force in one of the directions is not enough to push the spool. Given lack of spool seals in the design, I wonder if I am facing a worn spool that passes pilot oil such that net force is not enough to move the spool.

Another thing to note, is that most 3rd function valves I've seen require a lot of current (~4A at 12V), and I don't believe the controller is designed to handle such power to the solenoids. Guessing I am stuck with trying to find a pilot solenoid valve which takes low power to actuate. For reference, the solenoids were measured at ~28 Ohm, and they draw only ~400 mA of current when energized.

I would greatly appreciate any advice. Meanwhile, I will try to reach out to Parker to see if there is anything I can substitute this for.

 

[wateka]

I'm right behind (or ahead) of you. I've got a 1993 853 S/N 510126246 I just bought as well. I am overhauling everything in it and just took out the Apitech valve yesterday. My 853 hasn't been started in at least 10 years, hence the need to look at everything before I put it back together. I notice your serial number is ..350 and mine is ..246. I emailed Bobcat Customer Service and the only thing they could only tell me about mine was that it's a 1993 model.

I take pictures of everything as I disassemble it, so once I get started I'll post those to see if they help you as a comparison.

Separately, I just ordered the Char-Lynn drive motor seal kits:

Char-Lynn 6000 Series Bearingless Seal Kit CL-61239

Seal Kit CL-61239 for Char-Lynn 6000 Series Bearingless is always in stock at Oringsandmore.

www.oringsandmore.com

and have ordered new pistons and a seal kit for the hydrostatic pump.

US $60.00 | Seal Kit for Sauer MPV046 MPT046 M46 Piston Pump

60.0US $ |Seal Kit for Sauer MPV046 MPT046 M46 Piston Pump| | - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

a.aliexpress.com

US $56.00 | Piston Shoe MPT046 MPV046 M46 Pump Parts for Repair Sauer Hydraulic Piston Pump

56.0US $ |Piston Shoe MPT046 MPV046 M46 Pump Parts for Repair Sauer Hydraulic Piston Pump| | - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

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[slik rik]

I'm right behind (or ahead) of you. I've got a 1993 853 S/N 510126246 I just bought as well. I am overhauling everything in it and just took out the Apitech valve yesterday. My 853 hasn't been started in at least 10 years, hence the need to look at everything before I put it back together. I notice your serial number is ..350 and mine is ..246. I emailed Bobcat Customer Service and the only thing they could only tell me about mine was that it's a 1993 model.

I take pictures of everything as I disassemble it, so once I get started I'll post those to see if they help you as a comparison.

Separately, I just ordered the Char-Lynn drive motor seal kits:

Char-Lynn 6000 Series Bearingless Seal Kit CL-61239

Seal Kit CL-61239 for Char-Lynn 6000 Series Bearingless is always in stock at Oringsandmore.

www.oringsandmore.com

and have ordered new pistons and a seal kit for the hydrostatic pump.

US $60.00 | Seal Kit for Sauer MPV046 MPT046 M46 Piston Pump

60.0US $ |Seal Kit for Sauer MPV046 MPT046 M46 Piston Pump| | - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

a.aliexpress.com

US $56.00 | Piston Shoe MPT046 MPV046 M46 Pump Parts for Repair Sauer Hydraulic Piston Pump

56.0US $ |Piston Shoe MPT046 MPV046 M46 Pump Parts for Repair Sauer Hydraulic Piston Pump| | - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

a.aliexpress.com

Tell us how those parts from alie took to show up and quality please.

Also does your pump have both drive motor feeds off the front/ towards front? If so what was the tag saying on your pump, mine was missing, and LPS had wrong pump as exchange. Also is the pump an mpt or mpv, because the manuals I have been finding dont show a dual port on one side of the pump.

 

[wateka]

Tell us how those parts from alie took to show up and quality please.

Also does your pump have both drive motor feeds off the front/ towards front? If so what was the tag saying on your pump, mine was missing, and LPS had wrong pump as exchange. Also is the pump an mpt or mpv, because the manuals I have been finding dont show a dual port on one side of the pump.

Quality looks good, but I haven't put the unit back together yet. I ordered the items on July 5th and they arrived via UPS on July 19th. Shipping isn't cheap, but the total cost is still far less than any option I could find here in the US.

If you order from AliExpress, I suggest paying via PayPal because trying my credit card on an overseas mail order transaction resulted in a security denial. PayPal was easier than calling my credit card company's customer service.

As for drive motor feeds, one of the feeds comes out of the back and then u-turns to the front, as shown in the picture. My data plate is also attached if that helps.

 

[slik rik]

Thanx for the pics, yeah mine has both ports on the front of the pump and all the suction hoses are on the back. You should start a thread on your rebuild

 

[wateka]

Hi, I recently purchased a Bobcat 853 (SN# 510126350) equipped with the Apitech front auxiliary control valve, but discovered that the valve only operates in one direction. Front auxiliary electronics are working fine, and both solenoids receive 12V power when function is triggered by the switches. I also ruled out the solenoid malfunction by swapping the solenoids. There is no audible change in engine / load when malfunction is observed, and so it seems the problem is with the valve body itself.

The service manual is silent with respect to "rebuilding" the Apitech valve, which is now obsolete. The parts diagram shows the solenoids (#27) and pilot orifice (#26) as separate parts, and also states that the replacement solenoids have an an orifice build-in and the separate orifice (#26) needs to be removed when replacing the solenoids. In my assembly, the orifice is built into the solenoid (tiny ruby orifice), so I imagine it was replaced at some point. I tried to see if maybe there was an old separate orifice left in the assembly which could be plugged, but nothing fell out of the solenoid port, and I could not pull anything out with a seal pick.

I am speculating that the following root causes could exist:

1. Pilot port delivering hydraulic fluid to the spool is obstructed
2. Spool rod is obstructed / has high resistance in one direction

My options as I see them, are:

1. Tear down existing valve, and attempt repair by cleaning / blowing all the passages with compressed air, and and replacing whatever seals I can still source from Bobcat, McMaster, etc.
2. Contact Parker (who purchased Apitech) and see if they have some alternative valves in the same form factor
3. Replace with a different directional valve (i.e. Eaton) that matches or exceeds specifications of the original Apitech

I am wondering if anyone else has observed a similar issue, or has recommendations on rebuilding these units in the absence of readily available parts. I will appreciate any advice on the matter.

 

[wateka]

I just posted my Apitech rebuild pics that may be helpful for your rebuild.

Pictures of 853 Apitech auxiliary valve rebuild

I finished the Apitech auxiliary valve rebuild for my 853. I'm no mechanic, so I take lots of pictures to help me put things back together. I made a slideshow of all the pics and uploaded it here:

www.skidsteerforum.com

 

[TL Johnson]

Some helpful tips and direction on this post. I have a 853, all functions work other than the Auxiliary. Replaced handle assy as it was bad to begin with from past owner, and module would not test out so I replaced it, still nothing. Any recommendations?

 

[ags_virginia]

Figured I would provide an update as to where things have been left off with respect to the original post.

Because Pulsar pilot valves are no longer available and servicing now obsolete Apitech aux valve is no longer possible, I decided to do a retrofit using the off-the-shelf ARGO-HYTOS RPE3-063C11-01200E12A ($162) direct-acting valve. The direct acting valve requires more electric power, so I will also be incorporating a separate bank of relays which can be triggered with existing low-current Bobcat controls.

My intent is to use a standard side-ported D03 backplate fitted with appropriate hydraulic fittings to accept the existing hoses. If that doesn't work, I may consider making a custom manifold designed with ports in the same location as in the original Apitech valve.

I will provide an update once things start falling into place.

 

[FJRDarksider]

My 853 is a 1993 as well. S/N # ......410
I am presuming mine has the same Apitech valve.
Just picked up a dozer blade (hydraulic pivot) so I'll see if mine works or not LOL
Wateka....I have used your photos on several occasions so thanks for posting those!