Hydro Pneumo Web Aligner System
A hydro pneumo web aligner is an edge guiding unit that senses the web edge with a low pressure air stream and corrects the web position with a hydraulic cylinder. The KEW hydro pneumo web aligner system is supplied as a complete power pack kit with a 0.5 HP motor, air sensor, filters, pipes and a cylinder of 4, 6 or 8 inch stroke.
Krishna Engineering Works makes its web aligners in house in Ahmedabad, India. This page describes the hydro-pneumatic unit part by part: the air sensor, the power pack, the cylinder and the kit, with the published data for each.
What is a hydro pneumo web aligner?
A hydro pneumo web aligner is a web guide in which the signal is pneumatic and the force is hydraulic. Air does the sensing because it is clean, safe and does not touch the web. Oil does the moving because it gives a large, stiff force from a small cylinder.
Nothing electronic sits between the sensor and the valve. The air pressure from the sensor acts directly on the hydraulic control valve of the power pack. The only electrical part is the motor of the power pack.
This makes the unit simple to understand and to maintain. A fitter who can keep oil clean and air flowing can keep it running. If you are still deciding between this unit and the photocell based electro-hydro unit, the web guiding system page compares the two.
How does the hydro pneumo web aligner work?
The hydro pneumo web aligner works as a continuous loop between the air sensor and the cylinder. The steps are:
- Low pressure air passes through the air filter and the air pipe to the sensor.
- The sensor is a fork. Air leaves one arm and is caught by the other, and the web edge sits in the gap between them.
- When the web covers half the gap, the pressure that returns from the sensor is at its mid value and the valve is balanced.
- If the web drifts further in, less air returns. If it drifts out, more air returns.
- The change in pressure moves the control valve, which sends oil to one side of the hydraulic cylinder.
- The cylinder shifts the unwind stand, rewind stand or steering frame until the edge is back at the middle of the gap.
- The pressure returns to its mid value, the valve closes and the cylinder holds its place.
This is a proportional control system: a small error gives a slow correction and a large error gives a fast one, up to the follow up speed of the power pack.
The parts of the hydro pneumo web aligner system
The system has four working parts: the air sensor, the power pack, the hydraulic cylinder and the adjuster. Each is described with the data Krishna Engineering Works publishes.
Air sensor
The sensor is a non-contact air flow sensor. It works at an air pressure of 5 to 28 mbar, infinitely adjustable, which is a very low pressure: enough to be measured, too little to disturb a thin film.
Because air flows out of the sensor all the time, dust and fibre are blown out of the gap, so the sensor is self cleaning. It is mounted on a fine adjustment bracket, which lets the operator move it to the web edge precisely when the web width changes.
An air sensor does not depend on colour or opacity. It reads clear film, printed film, paper and foil in the same way. Very open or porous materials let air pass through, so state the material when you enquire.
Power pack
The power pack contains the motor, the oil pump, the oil tank and the control valve. Two standard sizes are published, type KEW-17 and type KEW-30. The numbers match the tank capacity in litres. The oil types listed are Servo 32, Enklo 44 and Hydro 37.
The hydraulic unit on its own is described on the web aligner power pack unit page. The group’s site on hydraulic power packs covers power pack design more widely.
Hydraulic cylinder
The cylinder converts oil flow into the sideways movement of the stand. The kit includes one hydraulic cylinder with a stroke of 4, 6 or 8 inch. Across the web aligner range, cylinders are available from 2 to 18 inch stroke.
The published operating force, 260 kg for the KEW-17 and 389.5 kg for the KEW-30, is given for a cylinder of 50.8 mm diameter.
Adjuster
The adjuster sets how strongly the unit reacts to an edge error. It is used during setup to find the point where the stand corrects quickly without overshooting.
What is in the hydro pneumo web aligner kit?
The hydro pneumo web aligner system (power pack unit) is supplied complete, so it can be fitted without sourcing parts separately. The kit contents are as published.
| Item | Quantity or size |
| Motor | 0.5 HP |
| Air pipe | 5 metres |
| Oil pipe | 5 metres |
| Sensor | 1 piece |
| Adjuster | 1 piece |
| Air filter | 1 piece |
| Oil filter | 1 piece |
| Hydraulic cylinder | 1 piece, with 4, 6 or 8 inch stroke |
The 5 metre pipes set a practical limit on how far the power pack stands from the sensor and the cylinder. Shorter runs respond faster, so place the power pack as close to the guiding point as access allows.
Technical specification of the power packs
The table gives the published specification of the two standard power packs.
| Item | KEW-17 | KEW-30 |
| Motor rating (3 phase, 50 Hz) | 0.5 HP | 1 HP |
| Pump flow rate | 3.4 l/min | 5.8 l/min |
| Tank capacity | 17 litres | 30 litres |
| Oil type | Servo 32, Enklo 44, Hydro 37 | Servo 32, Enklo 44, Hydro 37 |
| Line pressure | 14 bar | 21 bar |
| Maximum operating force (50.8 mm diameter cylinder) | 260 kg | 389.5 kg |
| Maximum follow up speed | 30 mm/sec at 3.4 l/min | 40 mm/sec at 5.8 l/min |
| Air sensor air pressure | 5 to 28 mbar, infinitely adjustable | 5 to 28 mbar, infinitely adjustable |
| Weight including oil | 40 kg | 60 kg |
The 0.5 HP motor of the kit matches the motor rating of the KEW-17. Power units from 0.25 HP to 3 HP are made across the web aligner range for heavier or lighter duties.
Which cylinder stroke do you need: 4, 6 or 8 inch?
Choose the stroke from the largest sideways error the unit must correct, with a margin on both sides. The cylinder works from its mid position, so only half the stroke is available in each direction.
| Stroke | Travel each way from centre | Generally suits |
| 4 inch (about 100 mm) | About 50 mm | Well wound reels with small edge variation, intermediate steering frames |
| 6 inch (about 150 mm) | About 75 mm | Unwind and rewind stands on most converting machines |
| 8 inch (about 200 mm) | About 100 mm | Reels with badly stepped or telescoped edges, wide textile and tyre cord webs |
A stroke that is too short runs to its end on a bad reel and the guide stops correcting. A stroke far longer than needed costs space and gains nothing. If your reels are worse than these cases, longer strokes up to 18 inch are available.
Choose the power pack from the weight to be moved. Add the stand, the shaft, the chucks and the heaviest full reel, and consider how freely the stand rolls on its slides. The operating force must overcome that friction with margin.
Where is the hydro pneumo web aligner used?
The hydro pneumo web aligner is used wherever a web must enter a process on a fixed line. Krishna Engineering Works lists these machines as suitable for it:
- Rotogravure printing machines
- Lamination machines and coating machines
- Slitter rewinder machines
- Doctoring rewinding machines
- Paper machinery
- Textile machines such as batching machines and inspection rewinding machines
- Tyre cord machinery
On KEW’s own machines it is fitted at the factory. The heavy duty drum type slitter rewinder lists a pneumo hydraulic web aligner as its guiding system, and the doctoring rewinding machine has a movable unwind stage for a hydraulic web aligner.
In textile and tyre cord plants the air sensor has a particular advantage: the air stream keeps lint and dust out of the sensing gap. Long lines need guiding at several points, as set out on the tyre cord dipping plant equipment page. Where the web must be steered between sections and no stand can move, a tracking roller assembly carries the rollers that the cylinder moves.
How do you install and commission the unit?
The unit is installed on a stand that already moves freely, in a few steps. The general sequence is below, and the site on web aligner installation and tuning covers the fine points.
- Check that the stand slides sideways by hand over the full stroke. Free it before fitting anything.
- Place the power pack level and within reach of the 5 metre pipes. Fill the tank with one of the listed oils.
- Mount the cylinder parallel to the stand travel, with the rod at mid stroke when the stand is centred.
- Mount the sensor on its bracket, just after the first roller following the stand, with the fork square to the web edge.
- Connect the oil pipes through the oil filter and the air pipe through the air filter.
- Start the motor and stroke the cylinder fully both ways several times to bleed air from the oil.
- Thread the web and slide the sensor until the edge is at the middle of the gap.
- Run slowly and set the adjuster so the stand follows the edge without hunting, then check at full speed.
| Routine check | Why it matters |
| Oil level in the tank | Low oil lets the pump draw air and the correction turns jerky |
| Oil filter | A blocked filter slows the cylinder |
| Air filter | A blocked filter lowers sensor pressure and the unit loses sensitivity |
| Air pipe for kinks and leaks | A leak looks like a web error and pushes the stand to one side |
| Sensor gap | Scrap or tape in the gap blocks the air and drives the cylinder to its end |
| Stand slides | Sticking slides cause hunting that no adjustment cures |
Spares and service
Web aligners are made in house by Krishna Engineering Works, so sensors, filters, pipes, cylinders and power pack parts come from the maker of the unit. Installation support, spare parts and technical support are provided for customers in India and abroad.
See repairing and servicing for the service scope. Other guiding products, including the web aligner system overview, are listed on the products page.
What to send for a hydro pneumo web aligner quotation
The unit is matched to your machine. Send:
- Machine type and the guiding point: unwind, rewind or between sections
- Material, and whether it is solid, porous or open weave
- Web width range and line speed
- Weight of the stand with the heaviest reel
- Worst edge error of your incoming reels, to fix the cylinder stroke
- Distance available between power pack, sensor and cylinder
- Power supply
- Photographs or a drawing of the stand and its slides
Send these through the contact page, and KEW will confirm the power pack and cylinder stroke.
Frequently Asked Questions
What is a hydro pneumo web aligner system?
A hydro pneumo web aligner system is an automatic edge guide that senses the web edge with low pressure air and moves the web with a hydraulic cylinder. The air signal from the sensor pilots the hydraulic valve directly. KEW supplies it as a power pack unit with motor, pipes, sensor, adjuster, filters and cylinder.
What does the KEW hydro pneumo web aligner kit include?
The kit includes a 0.5 HP motor, 5 metres of air pipe, 5 metres of oil pipe, one sensor, one adjuster, one air filter, one oil filter and one hydraulic cylinder with a stroke of 4, 6 or 8 inch. It is supplied complete, so the unit can be fitted to a machine without buying other parts.
What air pressure does the air sensor use?
The air sensor works at 5 to 28 mbar, infinitely adjustable, according to the published specification. This is far below factory compressed air pressure. The low pressure means the air stream does not deflect a thin web, while the constant flow keeps dust out of the sensing gap, which is why the sensor is described as self cleaning.
Which cylinder stroke should I order?
Order the stroke that covers your worst edge error on both sides of centre. The cylinder works from mid stroke, so a 6 inch stroke gives about 75 mm of travel each way. The kit is offered with 4, 6 or 8 inch stroke, and cylinders from 2 to 18 inch stroke are available across the range.
What is the difference between the KEW-17 and KEW-30 in this system?
The KEW-17 has a 0.5 HP motor, a 17 litre tank, 14 bar line pressure, 260 kg maximum operating force and a follow up speed of 30 mm per second. The KEW-30 has a 1 HP motor, a 30 litre tank, 21 bar, 389.5 kg and 40 mm per second. The larger unit moves heavier stands faster.
Does the hydro pneumo web aligner work on transparent film?
Yes, an air sensor reads the physical edge of the web, so it does not matter whether the film is clear, tinted, printed or metallised. This is one reason converters choose a hydro-pneumatic unit for clear films. Very porous or open materials are different, because air passes through them, so name the material in your enquiry.
What maintenance does the unit need?
The unit needs clean oil, clean air and a free moving stand. Check the oil level, the oil filter and the air filter regularly, keep the sensor gap clear of scrap, and inspect the air pipe for kinks or leaks. Use only the listed oil types: Servo 32, Enklo 44 or Hydro 37.
