In this installment of the manroland Goss web systems Americas educational series, we look at the basic operation and some easy troubleshooting tips for Graco series progressive divider valve assemblies that are commonly used for automated grease distribution across Goss legacy presses.
Graco Grease Pump Troubleshooting
How do they work?
Most systems have multiple divider valve assemblies fed by a single pump. A divider valve assembly receives grease pumped from a reservoir and delivers the grease in specific doses to lubrication points, such as bearings and bushings. The assembly may also feed a second divider valve assembly.
Typically, a programmable logic controller (PLC) will initiate a grease cycle at pre-set intervals, usually measured in print impressions. When the cycle is initiated, the grease pump will start and the feed valve for one of the primary divider valve assemblies in the system will open. The feed valve (shunt valve) can be a stand-alone valve placed in the feed line to the divider valve assembly or can be an integral component of the assembly itself.
Grease continues to be fed to the assembly until a pre-determined time controlled by the PLC has elapsed. Alternatively, many primary divider valve assemblies include a “end-of-cycle” detection switch, which signals the PLC to close the feed valve and open the feed to the next assembly in the system.
The assembly is made up of multiple blocks, each block containing passages and a spool valve that simultaneously opens and close the passages as it moves back and forth.
Each spool valve is sized to deliver a specific volume of grease on each stroke. Some valve blocks are “cross-ported” to double the output of an individual block.
Other than the inlet shunt and the end-of-cycle detector, the sequential functioning of the spools that comprise an assembly is a result of a clever mechanical design that requires no electricity.
Typical 7 Block Divider Valve Assembly
Typical System Architecture
Pictured below is a very high-level representation of a system layout. The pump is feeding a central trunk line. We see four assemblies attached and the trunk line going off the page to supply more assemblies. The assemblies Master 1 and Master 2 are controlled with shunt valves and end-of-cycle switches. The two assemblies in series on the left are fed by a time-based shunt valve. These two assemblies are located inside a rotating cylinder so it was desired to avoid electrical control elements.
Grease pumps typically have attached to their outlet an over-pressure sensor that communicates to the PLC, a pressure gauge and a relief valve.
When there is a blockage in the system, the over-pressure is communicated to the PLC and is associated with the individual shunt valve open at the time. That shunt is closed and the next divider assembly in the circuit is opened, dropping the pressure at the pump.
A fault message is posted to the operator which is the first clue to the source of the problem. On rare occasions, all the assemblies in the circuit could fault on the same cycle. This could indicate a blocked or crushed primary feed line.
Grease Fault Indicators
The first step to solving a blockage is to examine the divider assembly indicated by the fault message. Divider assemblies are equipped with individual over-pressure indicators for each feed port. The most common type is the manually re-settable pin indicator. The pin will extend about 6mm (1/4”) when there is a blockage. The pin stays out even if the pressure is relieved and is re-set simply by pushing with your finger. Pictured at right is the less common simple relief type that also gives a visual indication.
Solenoid Actuated Shunt Valve Assemblies
If you have a grease fault message but there are no indicator pins sticking out, you might suspect the shunt valve. The assembly-mounted shunt valve is opened to feed grease by a solenoid and returned to the closed position by a spring. To test if the valve is sticking, look at the end of the solenoid opposite the valve (red arrow below). There is a round pin in the center. Press in on the pin with a blunt tool of a smaller diameter. When you relieve force on the pin the spring should return the valve immediately, otherwise, the valve is sticking and must be addressed. If the valve appears to be free then the solenoid may be weakening and needs to be replaced. Another check for this is to hold the valve open while a manual grease cycle is initiated. If the assembly completes its cycle when you are manually holding the valve open then you have confirmation that the valve or solenoid is the source of the fault.
More Diagnostic Techniques
It is not recommended to initiate more than a few manual grease cycles with the machine sitting idle. This has even been known to force the shields off of cam followers. An alternative for investigating an individual divider assembly is to remove the grease feed line from the assembly and replace it with a fitting for a manual grease gun. A grease gun fitted with a pressure gauge of at least 1,500 psi (100 bar) is ideal. Now the function of the divider assembly can be investigated either in the machine or on the bench.
Progressive divider valve assemblies are very complex and performance can be influenced by many factors.
For example, if air is introduced into the feed lines it can lead to malfunctions, especially if the system back-pressure is high.
Grease contamination, including mixing of incompatible greases in the system, can also cause serious performance issues. Machines that are re-started after being taken out of production for an extended period can present challenges as well.
Due to the complexity of these automatic lubrication systems, we strongly suggest you always refer to the manufactures operating, maintenance, and safety instructions.
Our team of engineers and service technicians are familiar with Grease Distribution Divider Valve Assemblies of all models and on various types of equipment and are available to support you.
Contact us for more information about Graco grease pump troubleshooting.