Hydro Pneumo Web Aligner Manufacturer & Supplier

A hydro pneumo web aligner is an edge guide that senses the position of the web with a low pressure air jet and corrects it with a hydraulic cylinder. Krishna Engineering Works builds the hydro pneumo web aligner in Ahmedabad, with an air sensor that works at 5 to 28 mbar and a power pack in 0.5 HP and 1 HP models.

What is a hydro pneumo web aligner?

A hydro pneumo web aligner combines two fluids, each doing what it does best. Air does the sensing, because a gentle air jet can detect a web edge without touching it. Oil does the moving, because oil under pressure can shift a loaded reel stand smoothly and hold it firmly.

The name is written in several ways: hydro-pneumo, hydro-pneumatic and pneumo-hydraulic all mean the same arrangement. What sets it apart from an electronic guide is that the signal between the sensor and the valve is air pressure, not an electrical signal. The only electrical item in the basic loop is the motor of the power pack.

How does air sensing work?

The air sensor reads the web edge by measuring how much of an air jet the web blocks. The steps below describe the loop used in hydro-pneumatic guides of this type.

1. 1. A fork shaped sensor sits astride the web edge. One arm blows a soft stream of air across the gap and the other arm receives it.

1. 1. The web edge partly covers the stream. When the web moves further into the fork the received pressure falls, and when it moves out the pressure rises.

1. 1. A small pipe carries the received pressure to the power pack, where it acts on a diaphragm connected to the servo valve.

1. 1. A spring on the other side of the diaphragm represents the set point. With the edge half way across the jet, air and spring balance and the valve is closed.

1. 1. Any change in the air signal tips the balance, the valve opens in that direction and oil flows to the cylinder.

1. 1. The cylinder moves the stand, the edge returns to the half covered position and the valve closes.

The loop is a simple example of pneumatics used for measurement, not for power. The pressures are tiny, at most a few hundredths of an atmosphere, so the jet does not disturb even a thin film.

Why sense with air and move with oil?

Air sensing is chosen for what it ignores, and hydraulic correction for what it can carry. The combination has held its place in converting plants for practical reasons.

• • It does not care what the web looks like. The jet is blocked by clear film, printed film, metallised film, paper and foil alike. Colour, gloss and transparency make no difference.

• • It keeps itself clean. Air flows outward from the sensor ports all the time, so paper dust and fibre are blown away from the sensing gap instead of settling in it.

• • It carries no electrical signal at the sensor. The sensor head and its pipe contain only air, which is one reason this type is common beside solvent based printing and coating units.

• • It is simple to understand and repair. A blocked pipe, a torn diaphragm or a dirty filter can be found and put right by a plant fitter without electronic test gear.

• • It moves heavy loads smoothly. The hydraulic side gives high force from a small cylinder and holds the stand rigidly between corrections.

The oil side is the standard KEW unit, described in full on the hydraulic power pack page.

Hydro pneumo web aligner specifications

The aligner is built on the KEW-17 or KEW-30 power pack. The published figures for the two are below.

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
Follow-up speed	30 mm/sec	40 mm/sec
Air sensor air pressure	5 to 28 mbar, infinitely adjustable	5 to 28 mbar, infinitely adjustable
Weight including oil	40 kg	60 kg

The adjustable air pressure is the tuning control of the sensor. A stronger jet gives a firmer signal on heavy or fluttering webs, while a softer jet is kinder to very light films. The complete kit, with pipes, filters, adjuster and cylinder, is itemised on the web aligner unit page.

Where does a hydro pneumo web aligner suit best?

It suits lines where the web or the surroundings make optical sensing awkward, and where the load to be moved is substantial. The table sets common cases against the reason.

Application	Why air sensing fits
Clear and translucent packaging films	The jet is blocked by the film even though light passes through it
Printed webs with changing designs	The sensor reads the physical edge, not the print
Paper and board converting	Outflowing air keeps dust out of the sensing gap
Solvent based printing, lamination and coating	No electrical signal at the sensor head
Winding and rewinding machines	Simple, robust guiding of the unwind or rewind
Heavy unwind stands	Hydraulic force moves the full reel smoothly

Krishna Engineering Works names winding rewinding machines as a typical user of the hydro-pneumo unit. On a rotogravure press the same unit is found at the unwind and the rewind, as described on the page for the power pack on a rotogravure printing machine. Other machines are listed under power packs by machine.

Where is it not the right choice?

A hydro pneumo aligner is not ideal for webs that let air through or for guiding to a printed line. Knowing the limits avoids a poor installation.

• • Open and porous webs. Nets, open weaves and light non wovens let part of the jet pass, which weakens the signal. A denser edge or a different sensing method is needed.

• • Line and contrast guiding. An air jet cannot see a printed line. Guiding to print needs an optical sensor.

• • Very long sensor pipes. The air signal takes time to travel along the pipe. The supplied 5 metre pipe is a practical length, and much longer runs make the guide slow.

• • Strong draughts at the sensor. A fan or dryer exhaust blowing across the fork disturbs the jet. Shield the sensor or move it.

• • Centre guiding with varying width. Following the centre line of a web whose width changes needs two sensors and a suitable arrangement, so say so in the enquiry.

For these cases the electro-hydro web aligner uses a photocell sensor for the edge with the same hydraulic correction. The client’s web guide system site compares sensor types in detail.

Setting up the air side

Set the air side with the web threaded and at running tension. The oil side should already be filled, bled and checked for rotation.

1. 1. Fix the sensor fork on the adjuster so that the web runs through the middle of the gap without touching either arm.

1. 1. Check that the air pipe is pushed fully home at both ends and is not kinked, flattened or trapped.

1. 1. Set the sensor air pressure near the middle of its 5 to 28 mbar range to begin with.

1. 1. Slide the sensor until the web edge covers about half of the jet, then switch to automatic.

1. 1. Watch the guide follow a hand made disturbance. Raise the air pressure if the response is weak or wanders, lower it if a light web flutters in the fork.

1. 1. Lock the adjuster and mark its position for the job.

The web must be flat where it passes through the fork. Fit the sensor close after a roller, where the web is supported, and not in the middle of a long free span where it can flap.

Keeping the air and oil circuits clean

Cleanliness is the whole of the maintenance for this type of guide. Both circuits have small passages, and both are protected by a filter that must be looked after.

Interval	Air side	Oil side
Every shift	Check that the web runs centrally in the fork	Glance at the oil level
Weekly	Wipe the sensor ports, check the pipe for kinks	Look for weeping joints and note oil colour
When response slows	Clean or replace the air filter element	Check the oil filter and the oil grade
After any repair	Blow through the pipe before reconnecting	Bleed the cylinder and top up
When oil darkens or clouds	No action	Change the oil and the filter element

A slow, lazy guide is nearly always a filter, a kinked pipe or cold thick oil. A guide that swings from side to side is nearly always air in the oil, too much sensor pressure or play in the cylinder mounting. These are intervals of general practice, and a dusty plant will need shorter ones.

If a unit of any make can no longer be brought back by cleaning, the repairs and servicing department replaces worn parts with new ones. Indian and imported hydro-pneumatic web aligner power pack units are repaired at the factory in Ahmedabad.

Fitting the aligner into a guiding scheme

The hydro pneumo aligner is the working unit, and the guiding scheme decides where it acts. At an unwind it shifts the reel stand. At a rewind the sensor travels with the stand and the reel chases the web. In mid machine it tilts a tracking roller assembly. These arrangements are compared on the web guiding system page.

All of them rely on the same feedback idea: measure the edge, compare it with the set point, and correct the difference. The main brand site presents the product as the hydro pneumo web aligner system.

Supply and volume orders

Krishna Engineering Works has the capacity to supply 100 to 150 units per month and invites enquiries from machinery manufacturers who purchase hydro-pneumo web aligner units in bulk. Spares for the hydro-pneumatic web aligner unit are kept readily available, and each unit is given a continuous trial before dispatch.

What to send for a hydro pneumo web aligner quotation

Send the details below, so the sensor and the power pack model can be matched to the job.

• • Machine type and the guide position: unwind, mid machine or rewind

• • Web material, thickness or weight range, and whether it is porous

• • Web width range, and whether you guide to one edge or to the centre

• • Line speed

• • Heaviest reel and the type of stand or frame to be moved

• • Conditions near the sensor: dust, solvent vapour, heat, air movement

• • Distance from the sensor to the place where the power pack can stand

• • Make and model of any unit being replaced

Send the enquiry through the contact page. The rest of the range is on the hydraulic power pack products page.

Frequently Asked Questions

How does an air sensor detect the edge of a web?

An air sensor blows a soft jet of air across a gap and measures the pressure that arrives at the other side. The web edge sits part way across the jet and blocks some of it. When the edge moves in, the received pressure drops, and when it moves out, the pressure rises. That pressure change is the guiding signal.

What air pressure does the sensor of a hydro pneumo web aligner use?

The air sensor of the KEW unit works at 5 to 28 mbar and is infinitely adjustable within that range. This is a very low pressure, a small fraction of the pressure in a plant compressed air line. It is enough to give a clear signal while leaving thin film undisturbed as it passes through the sensor.

Can a hydro pneumo web aligner guide transparent film?

Yes. Air sensing depends on the film physically blocking the jet, not on blocking light, so clear, tinted, printed and metallised films all give the same kind of signal. This is one of the main reasons hydro-pneumatic guides are used on packaging film lines where optical sensors would need special settings for each material.

Does a hydro pneumo web aligner work on non woven or open fabric?

It works on dense non wovens and close fabrics, but open or very light webs let part of the air jet pass through them. The signal then becomes weak and the guide loses precision. For such webs describe the material in your enquiry, so that the sensor arrangement or an alternative sensing method can be proposed.

Is a hydro pneumo web aligner suitable near solvent based inks?

The sensing side is well suited, because the sensor head and its pipe carry only low pressure air and no electrical signal. The power pack still has an electric motor, so its position and electrical fittings must follow the safety rules for the area. Tell the supplier about the area classification when you