Fendt 720 free flow return problems?

[Blue.]

As the title anyone had trouble with back pressure?

I’m running a bent axis motor and it keeps blowing the shaft seal,lasted 3 hours today till it emptied the hydraulic tank

I’ve it piped up with flow and return in the spool and the case drain through the free flow return,did try both return and case drain through the free flow and that also blew the seal.

Tia Eulb...

 

[Deerefarmer]

When you shut the motor off are you using the float position to stop it?

 

[Andrew]

As the title anyone had trouble with back pressure?

I’m running a bent axis motor and it keeps blowing the shaft seal,lasted 3 hours today till it emptied the hydraulic tank

I’ve it piped up with flow and return in the spool and the case drain through the free flow return,did try both return and case drain through the free flow and that also blew the seal.

Tia Eulb...

Have you had a gauge in the return line to check for back pressure. Could be an obstruction in the pipe? Is the motor at the end of a long pipe run?

 

[principal skinner]

What size is the return line relation to the flow? Put a pressure gauge in the return line to see what’s going on.

Has the motor got an adjustable resistor? Are you using more oil flow than you need??

 

[Blue.]

When you shut the motor off are you using the float position to stop it?

Only turned it off the once today,after it had emptied the tank,have it set on hms to float stop.

Have you had a gauge in the return line to check for back pressure. Could be an obstruction in the pipe? Is the motor at the end of a long pipe run?

Never thought of using a gauge to check,pipe run is probably 15m.

 

[Blue.]

What size is the return line relation to the flow? Put a pressure gauge in the return line to see what’s going on.

Has the motor got an adjustable resistor? Are you using more oil flow than you need??

3/4” for return,1/2” for case drain.

Running spools at 70,possibility I’m running it with to much flow.

It’s a feed pump for an umbilical pump so the motors in the slurry pit,the 1st thing you know about a leak is an empty tank.

 

[Andrew]

3/4” for return,1/2” for case drain.

Running spools at 70,possibility I’m running it with to much flow.

It’s a feed pump for an umbilical pump so the motors in the slurry pit,the 1st thing you know about a leak is an empty tank.

If the motors in a slurry pit and a 15m pipe run there will be a fair bit of back pressure in the case drain. Last motor I dealt with was 10bar max on the case drain.

 

[Blue.]

If the motors in a slurry pit and a 15m pipe run there will be a fair bit of back pressure in the case drain. Last motor I dealt with was 10bar max on the case drain.

Max internal pressure 4 bar.

Bigger pipe on case drain needed?

 

[GFA]

Does your 720 have the separate return which I believe is for case drain looks like a brake coupler next to the free flow return

 

[Andrew]

Max internal pressure 4 bar.

Bigger pipe on case drain needed?

How far below the tractor is the motor? Maybe something more drastic is needed?

 

[Blue.]

Does your 720 have the separate return which I believe is for case drain looks like a brake coupler next to the free flow return

I think it does have a brake coupler type fitting,I’ll look tomorrow.

How far below the tractor is the motor? Maybe something more drastic is needed?

Can be upto 6m lower.

The pumps are sold to pump up from a depth,just possibly not for hours on end.

 

[Andrew]

I think it does have a brake coupler type fitting,I’ll look tomorrow.


Can be upto 6m lower.

The pumps are sold to pump up from a depth,just possibly not for hours on end.

I’d stick a pressure gauge in the drain at the motor and again at the tractor connection. Try and get an idea what’s going on.

 

[Mr Happy]

As the title anyone had trouble with back pressure?

I’m running a bent axis motor and it keeps blowing the shaft seal,lasted 3 hours today till it emptied the hydraulic tank

I’ve it piped up with flow and return in the spool and the case drain through the free flow return,did try both return and case drain through the free flow and that also blew the seal.

Tia Eulb...

Ok let's start at the beginning. How long have you had this item of machinery? When the the first seal blew who replaced the shaft seal and what type of shaft seal was used? Has the case drain flow been checked? As high case drain flow will increase the pressure inside the motor body causing the shaft seal to blow. Are the quick release couplingd in tip top condition? Sorry for all the questions but I presume it is a manufactured piece of farm equipment. Which has been ok for a time and now you are experiencing hyd motor problems.

 

[Pheasant Surprise]

Check pressure on the return line as @Andrew says.

I’d replace the quick couplers in the return line with new as they might be stuffed and increasing the back pressure significantly.

Also put a large(r) bore hose on the return to reduce the back pressure. 15m of pipe on and only max 4 bar back pressure is asking for trouble with 1/2” hose.

 

[Blue.]

Ok let's start at the beginning. How long have you had this item of machinery? When the the first seal blew who replaced the shaft seal and what type of shaft seal was used? Has the case drain flow been checked? As high case drain flow will increase the pressure inside the motor body causing the shaft seal to blow. Are the quick release couplingd in tip top condition? Sorry for all the questions but I presume it is a manufactured piece of farm equipment. Which has been ok for a time and now you are experiencing hyd motor problems.

Two new pumps less than 12months ago,both suffered same failure on same tractor.

New pipes,new couplings,replaced seals myself,seal is only a standard 55x72x8 seal would viton be better?

I bought the pumps from Finland so a bit of a language barrier,info supplied was “must use free flow return”.

I’ll check back pressure and return flow and report back.

 

[Mr Happy]

If you want to speak to the UK supplier for OMFB hyds contact Commercial Vehicle Hydraulics tel nr 01773 581983. Iam sure they will be able to advise on the correct shaft seal and may have them in stock..

 

[Pheasant Surprise]

Two new pumps less than 12months ago,both suffered same failure on same tractor.

New pipes,new couplings,replaced seals myself,seal is only a standard 55x72x8 seal would viton be better?

I bought the pumps from Finland so a bit of a language barrier,info supplied was “must use free flow return”.

I’ll check back pressure and return flow and report back.

Not on tractor, but on my 360 I’ve got a B&P variable swash bent axis piston motor and a deliberately oversized 1” free flow case drain line. It looks ridiculous but it works perfectly. B&P really go to town in their blurb emphasising the importance of a low pressure case drain.

The longer your case drain line, the bigger the bore you need to compensate. Put flow and return via the spool and the 3rd line case drain into the oversize case drain quick coupler on the rear of the tractor.

 

[davedb]

The massive pipe run will be creating some back pressure as it is especially brings it’s at a depth aswell the case pressure in the pump has to overcome the elevation aswell as the pipe length so I’d say a bigger bore pipe would be the only hope

 

[Mur Huwcun]

As daft as it may sound is there no way a venturi type valve is available to fit in the return line to create a vacuum effect in the case drain pipe to relieve the pressure?

 

[Blue.]

Tractor has the extra return line but it’s very small diameter piping behind the coupling,only looks 1/2” external.