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Maintenance Hydraulic Troubleshooting on Interactive CD

Our nationally acclaimed Maintenance Hydraulic Troubleshooting workshop on six fully interactive CD's.  Includes our MHT workshop manual.  6-CD Set - $1200 Individual CD's - $250 + Shipping and Handling.            Click on http://gpmhydraulic.com/mhtcds.htm to find out more. 

Troubleshooting Suspended Load Applications

With Pilot Operated Check Valves

Many cylinder applications where a load is either suspended or clamped requires pilot operated check valves to be used in conjunction with a float center directional valve. 

Underneath the directional valve is a set of pilot operated check valves and flow controls.  The purpose of the check valves is to lock oil in on both sides of the cylinder when the directional valve is de-energized.  When operating properly, these valves should hold the cylinder in place.  The reason the float center valve is used is to allow the pressure in the pilot lines of the check valves to bleed back to the tank.  This will allow the check valves to close and hold the load. The flow controls are connected in a meter out configuration and are used to control the speed of the cylinder.

There is a filter connected in the tank line of the valve manifold.  When the element is not contaminated oil that exhaust out of the cylinders will be filtered by this element prior to returning back to the tank.  When the directional valve is de-energized the pilot lines of the check valves are ported to the tank through the return filter.

Cylinders Are Drifting Up

  The fact that the Cylinders are drifting up obviously means that oil is flowing into the (full piston side) sides of the cylinders.  As with any single rod cylinder, there are more square inches of area on the full piston side than the rod side. This means that more force will be generated to raise the cylinders even if the pressure on both sides is the same.  The following can cause the cylinders to drift up:

Wrong Directional Valve Installed

  Although the numbers on the conduit housings may be correct, the actual valve on the machine may be of the “closed” center type.  There will be a small amount of oil that bypasses through from the “P” port through the internal tolerances to the “A”, “B” and “T” ports.  This would allow equal pressure to both sides of the spool.  The pressure will build up to ½ the pressure reading at the pump in each line.  For example, with the gauge at the pump reading 1100 PSI, 550PSI will be exerted on both the full piston and rod sides of the cylinders.  The higher force generated on the full piston side can cause the arm to drift up if high enough to overcome the weight of the load. 

One method of checking this is (with the pump off) to install a tee and pressure gauges in the lines connecting to the cylinder.  If the above mentioned pressure is read on both gauges then the wrong valve has most probably been installed.  Another method of checking the valve is to remove it from the machine and blow compressed air into the “T” port.  Air should flow out of the “A” and “B” ports if the valve has a float center.  If no air blows out of any port then the valve is most likely a closed center.

The Directional Valve is not Re-Centering

If the directional valve spool does not fully spring return to the float center position, then the valve would be partially open to the “A” or “B” position. This will allow oil to be ported to the full piston or rod sides.  With oil ported to the full piston side the arm will raise.  This can be caused by contamination in the valve or a weak spring.  If gauges were installed in the cylinder lines then there would be a high pressure reading on the gauge in the line to the full piston side and a low pressure reading on the other gauge.

The Return Filter Element is Contaminated

Some filters do not contain an internal bypass check valve. If the check valve exists and operating properly then once the inlet pressure reaches the check’s spring rating oil will bypass the element. The pressure in the return line would be the rating of the check valve spring, usually 25-50 PSI. If no check valve is present then the pressure in the return line would build to whatever is necessary to force the oil through the element.

  The internal bypassing from the “P” port across the spool mentioned previously will also direct a small amount of oil flow to the “T” port.  Any back pressure created by the filter or check valve will be equally transmitted through the “A” and “B” ports then to both sides of the cylinder.  Once again the arm can raise if the higher force in the full piston side is high enough to overcome the weight.  The same condition would exists if there is a restriction of some sort in the return line.

  The simplest test to make is (with the pump off) to remove the element from the housing.  This would remove any back pressure generated by the filter.  If the filter has not been changed within the last three months then I would recommend changing it.  There is a pipe plug on the right side of the filter housing where a gauge can be installed to monitor the back pressure.

Worn Manifold

  If there is a breach inside the manifold, oil could bypass from the pressure port to the “A” or “B” ports.  The same condition would occur if the check or flow control blocks were also badly worn.  If the problem still exists once the above mentioned tests are made and new components installed, then the manifold should be suspected.  By observing the gauges installed in the cylinder lines, a higher pressure would exist on the full piston side gauge if the manifold were worn.  The only known remedy for this is to replace the manifold.

Cylinders Are Drifting Down

  The fact that the Cylinders are drifting down means that oil is flowing from the (full piston side) sides of the cylinders back to tank.  Hydraulic oil always takes the path of least resistance in a hydraulic system. The following can cause the cylinders to drift down:

  Wrong Directional Valve Installed

  Sometimes the float center directional valve gets replaced with a closed center valve. When this happens, the directional valve will close first blocking the flow to the cylinder when it is de-energized.  This will cause the check valves to stay open momentarily. Oil will then slowly by-pass across the tight tolerances inside the valve. This results in the cylinders only drifting for a couple of inches and then stopping once the check valves finally close.

  You should not ever assume that the valve plate is the original one that came with the valve. Sometimes they get lost and replaced with another.  One method of checking the valve is to remove it from the machine and blow compressed air into the “T” port.  Air should flow out of the “A” and “B” ports if the valve has a float center.  If no air blows out of any port then the valve is most likely a closed center.

  Dirty Check Valves

 Since check valves will get a 100% seal, this makes them the ideal component to use in these type of applications. However, check valves normally fail in the open condition due to contamination. With the pump off, they can be easily removed, cleaned and re-installed.

  Worn Cylinders Seals

If the above is checked and the cylinders are still drifting down, the cylinder seals are probably worn. Worn seals will allow the oil to by-pass the pistons.  This is the best way to check cylinder seals. With the pump off, the rod side line can be removed. Turn the pump on and fully extend the cylinders until they bottom out. Any by-passing can be checked at this time.

Al started off the month spending Super Bowl Sunday consulting with a box plant on their Corrugator Rollstand Hydraulics.  Afer a 13 hour day, he made it home just in time for the 4th quarter!  The following week he was back at the same plant, this time cleaning the hydraulic unit with GPM's 1 Micron, Flushing Machine. The 2nd week in February he worked with Alan in Florence, South Carolina in one of GPM's largest-ever Maintenance Hydraulic Troubleshooting workshops.  The program was attended by a variety of industries; injection molding, die casting, steel, wood products and paper. The week of the 19th, Al was contracted by a machine manufacturer to analyze their systems at an Oriented Strand Board plant.  While in the office he worked on writing a "Troubleshooting Plywood Hydraulics" manual for an upcoming program in March. On March 5th, Al's off to work on his tan for a week's vacation in the Virgin Islands!

Alan taught a Troubleshooting Papermill Hydraulics class in Roanoke Rapids, NC and flew to Los Angeles to teach a Maintenance Hydraulic Troubleshooting workshop (and hang out around Sunset and Vine a little...) and another one at Chester Wood Products in South Carolina.  He had a consulting job at Grant Forest Products in Allendale, SC and teamed with Al at the monster MHT in Florence AL.  He hasn't done much motorcycle riding in the past month, but he did attend the International Motorcycle Expo at the Georgia World Congress Center.

Jack is finally in the office for a week after his seventh consecutive week in a row on the road!  Public seminars and consulting jobs all over the southeast have kept him traveling constantly.  He's spent as much time away as his motorhomes.

I've been doing the word processing and publishing of the manuals for upcoming customized workshops.  Coordinating all of the in-plant and public classes has kept me pretty busy, too.

3. In-plant consulting and troubleshooting

Nothing is more expensive than unscheduled down time.  GPM’s customers know they can call whenever they have a troubleshooting issue they simply can’t resolve.  With over 50 years experience dealing with hydraulic failures, our consultants have the resources to help troubleshoot whatever hydraulic problem you encounter.  Whether you’re experiencing a total system outage, repeated component failure or just need a professionally designed preventive maintenance schedule, the consultants at GPM can help.  Call GPM for     

            In-plant  Troubleshooting                                                

            Leakage Problems                                                         

            Pressure Settings

            Shock Problems

            Preventive Maintenance Scheduling

            Hydraulic Troubleshooting Manual Development

            Startup Consulting and Recommendations

            Heat Problems

            Repeated Component Failures  

            Speed Problems

Do you want to learn more on how GPM can help you? Go to http://gpmhydraulic.com/troubleshooting.htm

Troubleshooting Proportional Valves

The complete guide to troubleshooting and maintaining linear positioner circuits with electronically controlled proportional valves.  The same manual used in our acclaimed Troubleshooting Proportional Valves public seminar.

                    $49.95 + Shipping & Handling

To order this and other exciting products online, visit the GPM Store!

4. Operator Training

The operator is taught the basic function of the hydraulic operated equipment. The student learns the function of the hydraulic pump, valves and the task they perform. Actual screen shots from your equipment are used in the classroom to discuss the electrical cycles in detail.

Click http://gpmhydraulic.com/operatortraining.htm and find out more!

What our students say

I feel that this course is an absolute must if you will be running the press. The hydraulic system is much easier to understand now that I know what each component does each step of the way.

I will be able to help maintenance personnel troubleshoot hydraulic problems better with an operators point of view. Also, be able to troubleshoot hydraulic related quality issues. 

5. 2007 Public Seminars

Troubleshooting Proportional Valves Brochure pdf

Troubleshooting Proportional Valves 2007

8 Hour Course

Registration Fee $450.00 Per Person. 

Save $100 if attended in conjunction with our three-day Maintenance Hydraulic Troubleshooting workshop

Date	City	Location
March 20	Laurel, MS
March 22	Clanton, AL
April 13	Atlanta/Monroe, GA	Monroe Community Building 602 E. Church St. Monroe, GA
April 23	Lufkin, TX
April 24	Lufkin, TX
April 26	El Dorado, AR
April 27	El Dorado, AR
May 8	Smithfield, NC
May 9	Smithfield, NC
May 11	Newberry, SC
October 12	Ruston, LA
November 9	Atlanta/Monroe, GA	Monroe Community Building 602 E. Church St. Monroe, GA

Only $350.00 If Attending Our 3-Day Maintenance Hydraulic Troubleshooting Workshop The Same Week. (See 2007 MHT Schedule Below)

            Learn How To Troubleshoot and Maintain Linear Positioner Circuits with Electronically Controlled Proportional Valves