Monthly Archives: May 2013

Belt(s) won’t run? I’ll bet it’s not the pump.

Belt(s) won’t run?  I’ll bet it’s not the pump.

2 of 3 – Hydraulic

This is the second of three articles about Telebelt belt-related problems.

From time to time, I get calls involving a belt that won’t run, or runs very slowly.  The call I like the least is, “My feeder (or main) belt quit running.  I replaced the pump, but it still won’t run.”

With over 800 Telebelts in the field, we are looking at more than 2,100 piston pumps.  We don’t hear of pump failures very often.

So, again, I’ll bet it’s not the pump.

Rule # 1 – Check to see if it will run with manual control.  If it will, the problem is probably electrical or in the radio.  If not, it’s mechanical or hydraulic.

Things that stop belts:

  •  Mechanical problems
  • Electrical problems
  • Hydraulic problems
  • Truck or engine failure (this is beyond the scope of this series)

 

Let’s deal with hydraulic problems.  By now you should have observed Rule #1 and you know the problem is not electrical and you cannot run manually.

 

Is there any pressure on the belt circuit, main or feeder?

If one belt is working, but one is not, connect a 400 bar gauge to the “M” test port for the belt that is not working.  This is explained in your manuals in the maintenance section.

  • Always hook up the 400 bar gauge first.  If there is over 60 bar you will blow your 60 bar gauge.
  • If neither belt is working, double check that the driver-side PTO shaft is turning.  This is just about the only thing that could cause both belt pumps to quit together.
  • If the belt works under normal load but stalls under a very heavy load, a larger displacement motor might be required.  Example: Feeders have motors that deliver optimum output under normal conditions.  Extreme loads, i.e. paving, might require larger motors with more torque.  Use a pressure gauge to see if the belt stalls at full pressure (280 bar) or if it has no pressure when it quits.

 

Is there pressure below 60 bar?

  • If it is below 60 bar, connect your 60 bar gauge.
  • Disconnect the square plug on the motor control valve for the pump you are working.  Another way would be to pull the belt card or belt card fuse for the pump you are working on.  This will insure you are not getting a false reading from belt card zero.
  • You will now be able to read standby (low) pressure.

 

Is there pressure above 60 bar?

  • Disconnect the square plug on the motor control valve for the pump you are working.  Another way would be to pull the belt card or belt card fuse for the pump you are working on.  This will insure you are not getting a false reading from belt card zero.
  • When the pressure drops below 60 bar, connect your 60 bar gauge.
  • You will now be able to read standby (low) pressure.

Location of Valves and Power Plugs

 

 

 

 

Belt Card Location

Belt Card Fuse Location

 

Is the pressure below 20 bar?

Using the prssure setting procedure in the manual, set standby to:

  • All feeder belts – 20 bar
  • Main belts except TB and TBS 130/600 – 20 bar
  • Main belts TB and TBS 130/600 – 25 bar
  • Boom/Outrigger pumps – 22 bar

 

Are the standby pressures low or erratic?

  •  This could indicate broken springs or a stuck standby spool.  Lightly tap the control valve (compensator) with a hammer – this often frees stuck spools.
  • Screw the pressure adjusting screw all the way in – this will override broken springs.
  • If these steps don’t work, shut the machine off.  Release air pressure on pressurized tank units.  Remove the low pressure spool and check for contamination or scoring.
  • If you think you have a bad compensator, swap it with the other belt pump and see if the problem changes to the other circuit.  (This can’t be done with the 140CC main belt pumps on a TB-130)

Note:  Compensator (control valve) problems are often the cause of pump “failures.”  A pump with low or no standby pressure will not come on stroke.  Repairing or replacing the compensator often does the trick.

 

If the standby pressure can be set:
Using the procedure in the manuals, check and set high pressure.  All pumps are set to 280 bar for high pressure.

  • If high pressure cannot be reached, eliminate problems that can cause this:
    • Motor leakage
    • Piston packing leaks
    • Valve spool leakage
    • Counterbalance or relief valve leakage

 

If you get this far, it might actually be the pump
The only way to truly test a pump is with a flow meter.  Even a bad pump delivers flow until back pressure is applied. You can also get a rough idea of pump condition by checking function times.

  • Time your belts to determine belt speed
  • Compare this to the times recorded on the pump test page, in the front of your manual
  • Rule of thumb; Main belts usually run 900 feet/min when delivered.  Feeders usually run 1,000 feet/minute.  If you get a low reading, check the motor(s) to make sure they haven’t been changed to a higher displacement.
  • You can also use function times to determine changes in the boom/outrigger pump.
  • A flow meter can also be used to check leakage rates from the pump case drain.

Last minute update:

 

A problem, with a customer’s TB-130, has been plaguing all involved for the last month.  They shelled the boom/outrigger circuit pump.  This was a true pump failure; what we call “grenading itself.”

After cleaning the system and installing a new pump, the circuit would work for a short time, and then the pressure would drop off.  Pushing and releasing the clutch would bring the pressure back, and then it would drop off, again.  Compensators, inlet modules, WBV valves and a second pump were tried, without any change.  The customer even took parts off a working TB-110 and the problem remained.  Three of us, at Putzmeister, with over 100 years of combined experience were convinced it was a problem in the boom control valves.

In desperation, Alan went back to the schematic.  Something we had not considered jumped out at him; the contingency pump circuit.  This is the small electric motor and pump that allow the boom to be raised, so the cab can be tipped, if the engine won’t start.  It feeds the boom circuit through a check valve.  The check valve poppet had hammered itself out of shape and it was allowing circuit flow back through the small pump.

This reinforces: 1) the value of the schematic, 2) the K.I.S.S. theory and 3) the “I’ll bet it’s not the pump” statement.