Cat 320C 2 pump merge

[Harry Dart]

I need to combine the pump flows to the attachment (auxiliary) valve for a double-acting high-flow attachment. Looking at the hydraulic circuit, it looks like I could fit an electric or pilot operated diverter valve at pump 2, to supply the service spool at the load-hold check port. (Through an external check valve) to combine pumps 1 and 2.

I have done this on Hitachis and Sumitomos, but not a Cat as yet. Anybody had any experience with this?.

 

[YELLOMTLMILITIA]

I need to combine the pump flows to the attachment (auxiliary) valve for a double-acting high-flow attachment. Looking at the hydraulic circuit, it looks like I could fit an electric or pilot operated diverter valve at pump 2, to supply the service spool at the load-hold check port. (Through an external check valve) to combine pumps 1 and 2.

I have done this on Hitachis and Sumitomos, but not a Cat as yet. Anybody had any experience with this?.

dont Cat machines have cross-sensing pumps anyway?

 

[John C.]

As I recall the auxiliary spool only gets one pump. Two pump flow is only on boom and stick. The machine cross flows in travel as I recall. I like the idea of trying to dump the second pump beyond the aux spool to run something. The problem is what is going to stroke up the second pump? Since you are taking the flow between the valve and pump I would assume the pressure would come out of the negative flow line but I was told that line is also load sensing.

What are you trying to run. I have swapped the stick at times with the bucket function and run log processors with the stick circuits.

 

[WhyWhyZed]

I think what you want to do, is shift the Boom II spool, but from the opposite pilot port as the boom raise function shifts it.
Boom II only adds 2nd pump oil when raising, not lowering, so what cat does for 2 pump attachments, is shift the boom 2 spool the other way.... where it has a "dead" land that simply blocks the open center path for that pump. That way, NFC pressure drops, and the 2nd pump strokes up.
Then you simply tee in to the discharge line of the 2nd pump and add that to the load check at the ATT spool.
That's how Cat did it on the B series - and from a glance at the C schematic, it appears they would do it the same on a C.

 

[Per Eriksson]

Whats your serial# ?

Cat just add a section on the end of the valve body when doing the 2 pump flow thing.

 

[Harry Dart]

I think what you want to do, is shift the Boom II spool, but from the opposite pilot port as the boom raise function shifts it.
Boom II only adds 2nd pump oil when raising, not lowering, so what cat does for 2 pump attachments, is shift the boom 2 spool the other way.... where it has a "dead" land that simply blocks the open center path for that pump. That way, NFC pressure drops, and the 2nd pump strokes up.
Then you simply tee in to the discharge line of the 2nd pump and add that to the load check at the ATT spool.
That's how Cat did it on the B series - and from a glance at the C schematic, it appears they would do it the same on a C.

The only suggestion I got from Cat was to fit an extra slice ($$$) into the main valve at the cab side, and tee the pressure and pedal pilots across. That makes for a lot of extra hoses etc in my opinion. I'll have another good look at the schematic, your idea sounds good, and I could still fit an electric selector into the boom 2 spool line to select 1 or 2 pump flow to att.

Thanks for that, I'll let you know how it works.

 

[Harry Dart]

Whats your serial# ?

Cat just add a section on the end of the valve body when doing the 2 pump flow thing.

Thanks, I've been told that by Cat, just looking at other options at this stage.
(Purchase and importing costs to New Zealand are horrendous.)

 

[Per Eriksson]

How are you going to replace the internal load check valve with an external?
I don't see a simple solution to this.

How about calling the salvage yards for a machine to pull the added valve section from, surely there must be some burnt or rolled units around?
These sections are the same on almost every cat excavator ranging from 318C to 336D, then all you need is 2 pilotlines and 2 flow lines connecting to the excisting lines going up on the boom.

 

[CRAFT]

My 320CLU has a factory installed option of what they call hi-flow for aux hydraulic flow, like for a larger jack-hammer or hoe-pac ...... but when I was trying to to demand a 65gpm flow for a drum style mulcher it worked but it would stall easily when trying to operate the boom or stick ...... Cats solution to this was to install a "Priority Flow control Valve", or sometimes referred to as a Stanley Valve ..... it would keep the aux attachment going steadily ........ they did this on a 322C with the same Mulcher and it solved all of the problems ....... A caution ! .... its very pricey to add, the quote I got was $10,000.00+ ....... :drinkup

 

[Harry Dart]

How are you going to replace the internal load check valve with an external?
I don't see a simple solution to this.

I have done 312C's this way. The load hold check sits under the plug between A & B att ports. By removing the plug, spring and check, and fitting an in-line 3/4" check valve, you prevent any back-feed to the P2 supply. The attachments we are using are all motor driven, so the load hold isn't so important at the spool.

 

[WhyWhyZed]

just traced it out on the 320C...looks like the "other side" of BM2 will still work as ATT2 like Cat did on the B series.
if you follow bL4 on the schematic, you'll see the hose is connected to drain full time on machines without the 2 pump attachment lines gp.

If you remove that hose from drain, you can connect it to attachment pilot. Then, when you use the attachment, you'll also shift BM2 "up"(schematic up...might be down on the actual machine- Cat likes to draw schematics upside down). See how BM2 has 4 blocked ports on the bottom enveleope... well that's so it simply blocks the open centre path and dumps NFC to stroke that pump up. Then, if you tee in from the 2nd pump between pump discharge and the DCV, voila... there's full flow. You put that into the ATT load check and hope the ATT1 valve spool can deal with 2 pump flow - it could on the B series no problem.
If you want 2 pump flow for both ways on a double acting attachment, you'll need to add a shuttle valve to pressure that bL4 line either way.
Now... see that symbol at the aL4 end of the BM2 spool with the diagonal lines?... that symbol represents a physical stop. That stop is actually the BM2 pilot fitting. The fitting in that end of the cap is long- so long that it touches the BM2 spool to prevent it from shifting up normally...that would prevent you from using BM2 as ATT2. So, you would need to remove that fitting and replace it with a regular one, or grind it short. Cool thing is... you can custom grind it to give an "in between" flow (partial DCV shift) if you don't want the 2nd pump to give full...it's touchy though....

disclaimer: done lots of 320 and 320B series this way - and I have a 315B that has it set up like that from the factory (ball valves to configure)
I haven't done this on a C model that I can recall.

 

[Harry Dart]

just traced it out on the 320C...looks like the "other side" of BM2 will still work as ATT2 like Cat did on the B series.
if you follow bL4 on the schematic, you'll see the hose is connected to drain full time on machines without the 2 pump attachment lines gp.

Thanks for the reply, my supplied schematics shows bL4 going back to the Fine Control solenoid valve, but I can shuttle into it. Although, I haven't got the machine here yet, so it may not have one fitted.

If you want 2 pump flow for both ways on a double acting attachment, you'll need to add a shuttle valve to pressure that bL4 line either way.

Yes, A&B pedal pilots are shuttled already for a pressure sensor, I'll be fitting a 0-500psi pressure reducer to bL4 so the customer can vary his P2 output.

I should get the machine in next week.

 

[WhyWhyZed]

oh yeah...that's right - when you turn on fine control, or Tamping mode, it holds the BM2 against that stop fitting...prevents BM2 from shifting... I think they simply took that line away on the B series that had 2 pump flow attachment option.

 

[Harry Dart]

yeah, who needs it ?