Web aligner spare parts are the sensors, adjusters, filters, pipes, cylinders and seals that keep a web aligner and its hydraulic power pack guiding accurately. Krishna Engineering Works supplies spare parts of web aligner units from Ahmedabad, and spares for its hydraulic power packs and hydro-pneumatic web aligner units are kept readily available.
Which web aligner spare parts are supplied?
The spares follow the contents of the unit itself. A web aligner (power pack) unit is supplied with a sensor, an adjuster, an air filter, an oil filter, a 5 metre air pipe, a 5 metre oil pipe and a hydraulic cylinder of 6 inch stroke, and each of those items can be replaced when it wears or is damaged.
The table lists each part, its job, and the usual sign that it needs attention. The signs are those met in general service on guides of this type.
| Spare part | Job in the unit | Usual sign that it needs replacing |
| Sensor | Reads the position of the web edge | Guide drifts, or does not react to the edge |
| Adjuster | Holds the sensor and sets the guide point | Sensor will not hold its position, slide is loose or bent |
| Air filter | Keeps dust out of the sensing circuit | Weak or slow sensor signal |
| Oil filter | Keeps dirt out of the servo valve | Slow cylinder in both directions |
| Air pipe | Carries the sensor signal to the power pack | Kinked, flattened, cracked or hardened pipe |
| Oil pipe | Carries oil between the power pack and the cylinder | Weeping at the ends, chafed or swollen cover |
| Hydraulic cylinder | Moves the stand or frame | Scored rod, oil at the rod end, drift under load |
| Seals | Keep oil inside the cylinder and joints | External leaks, cylinder creeping when it should hold |
Sensors and adjusters
The sensor is the part of the aligner that sits closest to the web, so it is the part most often knocked, clogged or bent. On the hydro-pneumatic unit it is an air sensor, and on the electro-hydro unit it is a photocell.
An air sensor has fine ports that must stay open and square to each other. A fork that has been hit by a reel or a trolley may look sound and still give a poor signal, because the two arms no longer line up. A photocell fails differently: a scratched lens, a damaged cable or a loose plug. In both cases a spare sensor on the shelf turns a long stoppage into a short one.
The adjuster carries the sensor across the web so that the operator can set the guide point. Its slide and locking screw wear with use. An adjuster that cannot be locked lets the sensor creep, and the web creeps with it. The two sensing methods are described on the hydro-pneumo web aligner and electro-hydro web aligner pages.
Air filters and oil filters
Filters are the cheapest protection the unit has, and they are consumed in doing their work. Both circuits of an aligner have small passages, and both are guarded by a filter element.
The air filter protects the sensing circuit. As it loads with dust, less air reaches the sensor, the signal weakens and the guide becomes vague. The oil filter protects the servo valve, whose passages are the finest in the power pack. A loaded oil filter starves the valve, and the cylinder slows in both directions.
General practice is to change the oil filter element whenever the oil is changed and after any repair that opened the circuit. Never run the unit without an element to get through a shift. Dirt that reaches the valve does more damage in an hour than a blocked filter does in a month.
Air pipes and oil pipes
Pipes fail by ageing and by accident, and a failed pipe stops the guide completely. The unit is supplied with 5 metres of each, which lets the power pack stand clear of the web path.
An air pipe carries only a very low pressure signal, so the smallest leak or kink matters. A pipe flattened under a guard or hardened by heat gives a slow, weak signal that is easily mistaken for a sensor fault. An oil pipe works at line pressure and moves each time the stand moves. Look for chafing where it rubs on the frame, weeping at the end fittings and any swelling of the cover.
When you replace a pipe, keep to the original length and bore unless the layout has changed. A longer or narrower air pipe delays the signal, and a longer oil pipe slows the cylinder.
Hydraulic cylinders and seals
The cylinder is the working end of the aligner, and its seals are its wearing parts. A hydraulic cylinder holds the load on trapped oil, so worn seals show up as a stand that will not stay where it was put.
Two kinds of leakage occur. Oil on the rod or at the gland is an external leak, which is easy to see. Oil passing the piston inside the barrel is an internal leak, which cannot be seen: the cylinder becomes slow, loses force and creeps when the web pulls on it. Seals can be renewed if the rod and barrel are still smooth. If the rod is scored or bent, new seals will be cut again within weeks, and the cylinder itself should be replaced.
A bent rod usually points to a mounting fault. Check that the cylinder is in line with the direction of movement and that its end pins are free, or the replacement will go the same way.
Other parts of the power pack
The motor, pump and servo valve are long life parts, and they are normally dealt with as a repair, not as a counter spare. A worn pump or a sticking valve needs to be tested with the rest of the unit after it is fitted.
For that reason these items are best handled through the repairs and servicing department, where old parts are replaced with new ones at the factory. The function of each component is explained on the hydraulic power pack page. For guide frames, rubber rollers for tracking roller assemblies are also part of the range.
What to quote when ordering spare parts
Quote enough for the part to be identified without a second message. The steps below cover it.
- Name the unit: hydraulic power pack, web aligner unit, hydro-pneumo web aligner or electro-hydro web aligner.
- Give the model and motor rating from the nameplate, and any serial or order number marked on the unit.
- Name the part and the quantity, using the names in the table above.
- For pipes, give the length needed and say whether it is the air pipe or the oil pipe.
- For a cylinder, give the stroke and bore, and describe the end mountings.
- For a sensor, say whether it is an air sensor or a photocell, and describe the web it reads.
- Add clear photographs of the old part and of the nameplate.
- State the machine the unit is fitted to and how urgently the part is needed.
Send the list through the contact page. If the nameplate is missing or unreadable, photographs of the whole unit from two sides usually settle which model it is.
Which spares should a plant keep in its store?
Keep the parts that are consumed, and the parts whose failure stops the line. The grouping below is general maintenance practice, to be adjusted to the number of guides in the plant and the hours they run.
| Group | Parts | Why hold them |
| Consumables | Oil filter element, air filter element, hydraulic oil of the named grade | Used at every oil change and after every repair |
| Line stoppers | Sensor, air pipe, oil pipe | Easily damaged, and the guide cannot run without them |
| Wearing parts | Cylinder seals, adjuster | Wear slowly, and can usually be planned for a shutdown |
| Insurance items | Complete cylinder | Worth holding where one guide feeds a whole line |
A plant with several identical guides needs far fewer spares per guide than a plant with one. A plant with units of several ages should record the model against each machine, so that the right part is taken from the shelf.
Fitting a spare part without causing a second fault
Most repeat faults come from dirt and air let in while a part is changed. A clean, ordered method prevents them.
- Stop the motor, isolate the electrical supply and support the stand so that it cannot move.
- Wipe the area around the joint before opening it, so that dirt does not fall into the circuit.
- Cap or plug open pipes and ports at once.
- Blow through a new pipe before connecting it.
- Fit the new part, tighten the joints firmly and evenly, and remove every cap and plug.
- Top up the oil, start the unit and stroke the cylinder end to end several times to clear air.
- Check each joint for weeping, then set the sensor and return the guide to automatic.
- Recheck the oil level after the first shift.
If a new part does not cure the fault, stop and look wider. A new sensor will not correct a sticking stand, and a new filter will not correct a worn pump. Tuning and fault charts for aligners in service are covered on the client’s web aligner site.
Spare part or repair?
Fit a spare when one identifiable part has failed, and send the unit for repair when the fault lies inside the power pack or several parts are worn together. The table gives the usual split.
| Condition | Better route |
| Blocked filter, damaged pipe, knocked sensor | Spare part fitted at the plant |
| Leaking cylinder with a smooth rod | Seal set, or a replacement cylinder |
| Slow in both directions with a clean filter and correct oil | Repair: pump or valve wear |
| Moves one way only with a sound sensor signal | Repair: valve |
| Old unit with several faults at once | Repair and overhaul, or a new unit |
Where one tank feeds two or three guides, a single fault in the tank or pump stops all of them, so stock for double and triple power units deserves extra thought. The complete kit that the spares belong to is itemised on the web aligner unit page, and the whole range is on the product catalogue page.
Frequently Asked Questions
Which web aligner spare parts wear out first?
Filter elements are consumed first, because they are designed to load with dirt. After them come the parts exposed to knocks and movement: the sensor, the air pipe and the oil pipe. Cylinder seals wear slowly over a long period. The motor, pump and valve normally outlast all of these when the oil is kept clean.
What details are needed to order a spare sensor?
State whether the unit senses with air or with a photocell, give the model of the power pack from its nameplate, and describe the web the sensor reads. Add a photograph of the old sensor on its adjuster. With those details the correct sensor can be identified without further questions and sent the first time.
How do I know the oil filter needs changing?
The usual sign is a cylinder that has become slow in both directions while the oil level and grade are correct. As general practice, change the element whenever the oil is changed, after any repair that opened the circuit, and whenever the oil has darkened or turned cloudy. Do not wait for the guide to slow down.
Can I fit a longer oil pipe or air pipe than the original?
You can, but the guide will respond more slowly. A longer air pipe delays the sensor signal, and a longer oil pipe adds pressure loss between the pack and the cylinder. Both make the guide slower and more inclined to hunt. Keep to the original length unless the layout has changed, and mention any change when ordering.
Should I replace the cylinder seals or the whole cylinder?
Replace the seals if the rod and the barrel are smooth and straight. Replace the whole cylinder if the rod is scored, pitted or bent, because a damaged surface cuts new seals within weeks. Before fitting either, check the alignment of the mountings, since side load on the rod is the usual cause of early seal failure.
Are spares available for older KEW power packs?
Krishna Engineering Works keeps spares for its hydraulic power packs and hydro-pneumatic web aligner units readily available. For an older unit, send the model, the motor rating and photographs of the unit and of the part needed, so that the correct item can be matched. Photographs matter most on older units, where a nameplate may be worn or painted over.
Do spare parts cure a guide that hunts from side to side?
Not usually. Hunting is most often caused by air in the oil, sensitivity set too high, or play in the cylinder mountings and stand slides, and none of these needs a new part. Bleed the cylinder, reduce the sensitivity and check the pins first. Order parts only when a worn or damaged item has been found.