The Basics on Maintaining Pneumatic Equipment in Forest Product Plants
Viking Engineering machinery expert outlines a number of basic maintenance steps that companies should follow to keep pneumatic equipment running in top shape.
By Jim Gookin, Viking Engineering
Date Posted: 3/1/2011
Many pallet and lumber facilities regularly rely on pneumatic equipment to keep their operations running. This maintenance column focuses on the basic aspects of pneumatic machinery and maintenance steps you should take to reduce downtime and inefficiency.
As always it is important to contact your machinery supplier for procedures that are specific to your equipment and situation. Remember to lock out and tag it!
Filter Regulator & Lubricator
The main air supply for a piece of equipment is connected to a Filter, Regulator with gauge & Lubricator (FRL). A clean, dry and regulated air supply is required by most equipment manufacturers.
The filter can be as basic as a water separator to the highly efficient coalescing filter. Although the coalescing filter looks like a regular air filter, it handles contaminants differently. Air filters basically trap particles by a direct impact process. The air passes through a membrane leaving the solids behind. The particle size allowed to slip through the membrane is based on a micron rating of the filtering element. The higher the number, the larger the particle will get by. Coalescing filters use a combination of direct impact, interception and diffusion to clean the air. This three step process allows the filtering element to clean the air more effectively without substantially reducing air flow rates.
Lubricators, when used, allow a small amount of atomized lubricant to enter the air stream. The lubricant is used by valves and cylinders to reduce friction. New pneumatic systems actually discourage the use of oilers. Valves and cylinders have coatings already applied to reduce friction. Environmental concerns of atomized petroleum products are eliminated.
Electrically activated air valves are classified as single (shown), double or double detent. When the coil is activated, on a single or double valve, the spool shifts from its center location, and when the power is removed the valve shifts back to center. A detent type valve shifts when power is applied but stays even when power is removed. It will only shift again when power is applied to the opposite coil.
Most air valves have a manual activation feature so that you can tell if the valve is functioning. Remember that this procedure does not indicate the coil status. I always make a habit of checking valves without power applied to the system. The manual function will not override a valve when the coil is energized.
Most air valves can be disassembled and cleaned. During cleaning, inspect the spool for corrosion and damage. Replacement spools are generally not available. When re-assembling, use a very light air tool oil to lube the spool. Never use spray oils that make the surfaces tacky after application.
Single or double acting air cylinders are the most common types. Single acting cylinders have only one air hose attached at the base end and usually use a spring to return.
A double acting cylinder has two air hoses attached. One hose is on the base end and the other is attached to the rod end.
Checking an air cylinder to see if it needs to be rebuilt is very easy. When the cylinder is retracted, air pressure is applied to the rod end side of the piston. Remove the hose from the base end to see if any air is coming out of the open port. If there is an air leak, then rebuild or replace the cylinder.
Some cylinders have a magnetic strip on the piston. This strip will activate a sensor that is mounted externally to the cylinder. This strip is not replaceable, but removing the clevis pin and rotating the rod 180 degrees may allow the sensor to pickup an undamaged part of the strip.
Mufflers are used to reduce air exhaust noise levels and reduce contamination of air valves. Because of the fine noise filtering action, mufflers are very susceptible to plugging up, causing a restriction. A restricted muffler will cause a sluggish operation of air cylinders and valves. Mufflers can be cleaned using a parts washer and blown dry. Cracked or damaged units should be replaced.
Pneumatic Problems & Solutions
Air cylinders, plumbed in parallel, do not extend and retract at the same time. A critical area that is often overlooked is hose length. The length of each hose, to each cylinder, must be the same when measured from the air valve. A cylinder that is fed with a short hose will react faster than the cylinder with the longer hose.
Air blows out of the muffler on a bank of air valves all the time. Using needle nose pliers, pinch each air hose at the air manifold until the air leak changes or stops. Follow that hose from the valve manifold to the air cylinder. If the cylinder is retracted, remove the air hose at the base end as described earlier. If the cylinder is extended, remove the rod end air hose. Check for cylinder bypass.
If air blows out of the muffler on a bank of air valves all the time but the cylinders check out OK, the problem will be either a manifold gasket or a faulty valve. Start by manually activating each valve and listen for a change in the air leak. Check the gaskets or replace that air valve.
If an air cylinder sticks when retracting or extending, most likely it is a cylinder rod that is bent. Remove the piston and rod assembly from the cylinder bore. Check for straightness. Straighten carefully if possible or replace cylinder.
If a cylinder piston becomes detached from the rod, during the cylinder extend cycle, the rod and piston should stop mechanically before the piston contacts the end plate off the cylinder. If you are using the end plate to limit the cylinder stroke, then reducing cylinder travel speed via a flow control should help. During the retract cycle, air pressure pushes on the piston dragging the rod with it. If the rod resistance is too great, the piston will separate itself from the rod. Correct cylinder sizing and pressure application should lessen this issue.
If the air valve will work when manually spooling but not in automatic, a faulty coil or no electrical power applied to the coil is usually the cause. If equipped, watch to see if the indicator lights up. Use a meter to check voltage at the valve coil. If there is power applied, replace the valve coil if available; otherwise the entire valve will have to be replaced.
If several cylinders, connected to the same valve bank, work slower than normal, there is typically either a supply or exhaust problem. Starting with the supply, monitor the air pressure at the valve bank. If low, check incoming hoses for kinks or obstructions. If all of the supply air checks out, then pull the mufflers to test the exhaust. Clean or replace the mufflers as needed.
For reliable pneumatic systems just remember… keep it clean and keep it dry. For more information, contact Jim at 800-328-2403.
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