Water Blasting – Higher pressure washing with power

Dr. Summers Waterjet Blog

KMT Waterjet Systems Weekly Waterjet Series

Water Blasting – Higher pressure washing with power

In the last post, on surface cleaning, I showed how the jet from a fan nozzle spread very quickly once the water left the orifice. With this spread the stream got thinner, to the point that, very rapidly the jet broke into droplets. These droplets decelerate very rapidly in the air, and disintegrate into mist which rapidly slows down. That mist has little capacity but to get a surface wet, and thus, within a very short few inches, the jet loses power and the ability to clean.

How can we overcome this? Obviously the jet would work better if it could carry the energy to a greater distance. And the jet that does that (as we know from trips to Disney) is a cylindrical stream. In some parts of the cleaning trade this is known as a zero degree jet, to distinguish it from the fifteen degree or other angular designation of the fan jet nozzles that it is often sold with.

But the problem with a single cylindrical jet is that it has a very narrow point of application. Depending on the standoff from the nozzle to the target this will increase a little as the distance grows, but is still likely to be less than a tenth of an inch. That, by itself, would make cleaning a bridge deck a long and laborious job. But consider that if we spun the jet so that it is tilted out to cover a 15 degree cone, the same angle as the best of the fan jets, the water would travel further. With a good nozzle it is possible to extend the range to 3 ft, rather than the typical 4 inches of a fan jet.

Rotating water blasting waterjet cutting head spray graphic

Figure 1. The gain in performance when a fan spray is changed to a rotating cylindrical jet. (initially proposed by Veltrup, these are our numbers).

In both cases the water flows out of the orifice at the same volume and pressure. But with the rotating jet the water is able to carry the energy some 9 times as far. As a result the area covered is 9-times as wide, and the job is carried out faster.

You can also look at it another way. It takes only about 10% of the water and the power to clean the surface with the rotating jet, as opposed to the amount required to clean with the fan jet. This is even though the pump unit and the flow rates are the same in both cases. This is why, when you buy some of the smaller pressure washers, they include a nozzle that has a round orifice and which then oscillates within a holder. Not quite as efficient as a controlled movement, but at least it is a start.

Now, of course, life is never quite as simple as it at first appears. Because the jet is being rotated there is sometimes, if the jet is being spun fast enough, some breakup of the jet because of the speed of rotation. And so, in the above example, too high rotation speed would have a disadvantage. Doug Wright showed this in a paper he presented to the WJTA in 2007.

Water blasting rotating jet effectiveness

Figure 2. The effectiveness of a rotating jet, at two speeds and at different distances (Doug Wright 2007 WJTA Conference Houston).

On the other hand because the jet has to make a complete rotation before it comes back to the same point on the coverage width, if the lance is moving too fast relative to that turning speed, then the jet will miss part of the surface that it is supposed to be cleaning.

I can illustrate this with a sort of an example. To make it obvious the rotating jet has enough power to cut into the material that it is being spun, and moved over. If the rotation speed is too slow, relative to the speed that the head is moving over the surface, then the grooves cut into the surface won’t touch one another and small ribs of material are left in the surface. This is not a good thing, either from a cleaning or mining perspective. The material we were cutting in this case was a simulated radioactive waste, that an improved design later went on to extract as a “hot” material in a real world project. These materials tend to be unforgiving if they are not properly cleaned off.

Water blasting grooves in rotation speed

Figure 3. Cutting path into simulant showing the grooves and ribs where the rotation speed is not properly matched to the speed of the head over the surface.

There is another answer, which is becoming more popular for a couple of different reasons. If the pressure of the water is increased, then the jet will remain coherent for a greater distance, at a higher rotation speed. Going to a higher rotation speed, also brings in an additional change in the design of the cleaning head.

Water blasting cleaning head vacuum capture of debris

Figure 4. Cleaning head concept sectioned to show vacuum capture of the debris through the suction line after the jet has removed the material and washed it into the blue cylinder.

As the pressure increases, so the energy of the water and the debris rebounding from the surface increase. To a point this is good, since once they are away from the surface it is relatively simple, if the cleaning operation is confined within a small space by a covering dome, to attach a vacuum line to the dome, and suck all the water and debris into a recovery line. The surface remains relatively dry, all the water and debris is captured, and the tool can be made small enough, and light enough, that it can be moved either by a man or on the end of a robotically controlled arm. (The arm we designed the head for was over 30-ft long, which means that the forces from the jets had to be quite small).

With the higher pressure also comes the advantage that the amount of water that is required, for example to remove a lead-bearing paint from a surface, is much lower. If the water becomes contaminated by the material being washed off, then not only has the total volume to be collected, which is an expense, but it also must be stored and then properly be disposed of. And that may cost several times the cost of the actual cleaning operation, if the contaminant is particularly nasty. So reducing the volume of the water is particularly useful.

A friend of mine called Andrew Conn came up with the idea, for removing asbestos coatings from buildings, of tailoring the pressure and the flow from the nozzles, so that the amount of water required was just enough that it was absorbed by the asbestos as it was removed. Simplified and reduced the costs of cleanup, where that was a significant part of the overall price.

And speaking of using higher-pressure water, this means that there is no need for the abrasive additive, when cleaning say a ship hull. And that means that there is no need to buy, collect, and dispose of the abrasive during the operation.

Spent water blasting cleaning abrasive at a shipyard.

Figure 5. Spent cleaning abrasive at a shipyard.

There are other advantages to the use of high pressure water over abrasive when cleaning metal, and I’ll talk about that subject a little next time.

Labels:abrasive cleaning,cylindrical jets,fan jets,pressure washing,radioactive waste,range,rotating jets,rotational speed,traverse speed


Waterjet Technology-Pumps, Intensifiers and Cannons

Dr. Summers Waterjet Blog

KMT Waterjet Systems Weekly Waterjet Series

Waterjetting  – Pumps, Intensifiers and Cannons

When we say a rock is hard it means something different, in terms of strength, to the meaning when we say that we want an egg hard boiled. Terms have to be, and usually are defined through the way in which they are used. At the same time each trade, industry or profession has certain terms that it adopts for its own with more specialized meanings than those which we, in the general public, are familiar.

Ask someone on the street what level of pressure they consider to be “high” and they might answer with numbers that range from 100 psi to perhaps 2-3,000 psi. And yet, within the industry those pressures are really quite low, relative to those most commonly used in cleaning and cutting. High-pressure waterjet systems are now available for water jet cutting metals, that will generate streams that run continuously at 90,000 psi, and the highest pressure jet that we generated in the MS&T Laboratories was at around 10 million psi.

Within that very broad range some simple divisions make it easier to group the ranges and applications of the different tools that are now common within different parts of the industry. At the same time, over the period of my professional life, the technology has moved forward a long way. Consider that when I wanted to run at test at 50,000 psi back around 1970 I had to use this particular set of equipment.

Water Cannon firing 12 gallons of water

Figure 1. MS&T Water Cannon firing 12 gallons of water at 50,000psi.

The water cannon was made by cutting the end from a 90-mm howitzer, and threading a one-inch nozzle on the end. Smaller orifices could then be attached beyond that to give different flow combinations. The pressure to drive the cannon was generated by putting 2,000 gm. of smokeless powder in a cartridge, and then loading and firing the cannon. We had been given the mount, which rotates around two axes by the then McDonnell Douglas (now Boeing), who had used it to hold and move the Gemini spacecraft while they were being inspected.

The pressure divisions which were debated and agreed by the Waterjet Technology Association back in the mid 1980’s broke the pressure range into three separate segments, which described the industry at the time.

The first range is that of the Pressure Washers. Operating pressures lie at and below 5,000 psi.


Figure 2. A small pressure washer being used to clean a drain. (Mustang Water Jetters)

Figure 2. A small pressure washer being used to clean a drain. (Mustang Water Jetters)


These are the types of unit which are often found in hardware stores for use in homes, and while I won’t get into this until some later posts on safety, and on medical applications, it should be born in mind that it is possible to do serious injury even at these relatively low pressures. (Folk have been known to use the jets to clean off their shoes after work . . . need I say more – a waterjet cuts through skin at around 2,000 psi, and skin is tougher than the flesh underneath). At pressures below 2,000 psi these are often electrically powered. A gasoline motor is often used to drive the portable units that operate above that pressure range.

High-pressure units are defined as those that operate in the pressure range from 5,000 psi to 35,000 psi. The drive motors are usually either electrical or use a diesel drive, and units of over 250 horsepower are now available. Many of these units are known as positive displacement pumps. That is taken to mean that the pump, being driven by a motor at a constant speed, will put out the same volume of water, regardless of the pressure that it is delivered at (up to the strength of the drive shaft).

To ensure that the pressure does not rise above the normal operating pressure several safety devices are usually built into the flow circuit so that, should a nozzle block, for example, a safety valve would open allowing the flow to escape. Different flow volumes can be produced in larger units by placing a gear box between the pump and the motor. As the motor speed changes, for the same piston size in the pump, so the volume output changes also. However, because the pump can only deliver at a certain power the size of the pistons can also be changed so that, at higher delivery pressures the same motor will produce a lower volume of water. I’ll go into that in a little more detail in a later piece.

Figure 3. Section through a high-pressure pump showing how the crankshaft drives the piston back and forth in the cylinder block, alternately drawing low pressure (LP) water in, and then discharging high pressure (HP) water out.

Figure 3. Section through a high-pressure pump showing how the crankshaft drives the piston back and forth in the cylinder block, alternately drawing low pressure (LP) water in, and then discharging high pressure (HP) water out.

Normally there are a number of pistons connected at different points around the crankshaft, so that as it rotates the pistons are at different points in their stroke. The evens the load on the crankshaft, and produces a relatively steady flow of water from the outlet. (Which, in itself, is a topic for further discussion).

As the need for higher pressures arose the first pumps in the ultra-high pressure range (that above 35,000 psi) were intensifier pumps. These pumps are designed on the basic principal that the force exerted on a piston is equal to the pressure of the fluid multiplied by the area over which it is applied. Thus with a piston that is designed with two different diameters can produce pressures much higher than those supplied.

Figure 4. The basic elements of a waterjet intensifier.

Figure 4. The basic elements of a waterjet intensifier.

Fluid at a pressure of perhaps 5,000 psi is pumped into chamber C. As it flows in the piston is pushed over to the left, drawing water into chamber B. At the same time the water is chamber D is being pushed out of the outlet channel, but because of the area ratio, the delivery pressure is much higher. If, for example, the ratio of the two areas is 12:1 then the pressure of the water leaving the pump will be at 12 x 5,000 = 60,000 psi.

Over the years the materials that pumps are made from, and the designs of the pumps themselves have changed considerably, so that pressure ranges are no longer as meaningful as they were some 25-years ago when we first set these definitions, but they continue to provide some guidance to the different sorts of equipment, and the range of uses of the tools within those divisions, so I will use these different pressure range definitions in the posts that follow.

Posted by KMT Waterjet Systems 2013 all rights reserved.

Labels:high-pressure,intensifier,positive displacement,pressure washing,triplex,ultra-high pressure,water cannon

Waterjet Pumps – Pump Pressure is not Cutting Pressure

When I began this series I pointed out that whenever a waterjet is going to be used both the target material and the waterjet delivery system have to be considered, if the work is to be done well.

In the last four posts I have tried to emphasize the role of cracks and flaws in the way in which water penetrates into and removes material. It is easier to see this with large-scale operations, such as in the removal of large volumes of soil, but it equally holds true in the abrasive cutting of glass. Now in this next series of KMT Waterjet Blogs,  the focus is going to swing back to the ways in which high-pressure waterjets are developed, particularly in the different choices of equipment that can be used.

Because this KMT Waterjet Blog Series is meant to help folk understand how systems work, and through that, how to improve production and quality it will tend to shy away from putting a lot of formulae into the presentations. There is a reason that I, an academic, don’t like having students learn equations by rote. It is that it becomes, quite possible, to misremember them. If you are used to looking them up (particularly true in today’s computer world where formulae can easily be used to generate tables) then you are less likely to mis-remember the exact relationships, and to make a possible critical mistake.

But, as I showed in the third post, when the tables of jet flow, horsepower and thrust were generated, there are a few, critical equations that need to be born in mind. And the one that underlies the economics of many operations is tied up in the size of the power that is available to do the work. The basic power equation itself is relatively straightforward:

Waterjet Pump Pressure Formula

Figure 1. Relationship between hydraulic horsepower, pressure and flow.

But the calculation gives different values, depending on where the calculation is made in a circuit. To demonstrate this, let us use a very simple drawing of a flow circuit.

Figure 2. The components of a simple flow circuit. Water is drawn from the water tank, through the pump and delivered down a hose to a high-pressure lance, where the water is fed, through a nozzle and aimed at the target, where it does the work.

Figure 2. The components of a simple flow circuit. Water is drawn from the water tank, through the pump and delivered down a hose to a high-pressure lance, where the water is fed, through a nozzle and aimed at the target, where it does the work.

In the course of this small set of posts the different components that make up this circuit are going to be discussed in turn. But at the end of the first set I mentioned that in an early comparison of the relative cleaning performance of 10,000 psi waterjets of nominally equal power, and flow (10 gpm IIRC) there was a dramatic difference in the cleaning efficiency, as the Navy reported at the time.

Figure 3. Relative cleaning efficiency in areal percentage cleaned, of five competing systems in cleaning heat exchanger tubes in Navy boilers. (Tursi, T.P. Jr., & Deleece, R.J. Jr, (1975) Development of Very High Pressure Waterjet for Cleaning Naval Boiler Tubes, Naval Ship Engineering Center, Philadelphia Division, Philadelphia, PA., 1975, pp. 18.)

Figure 3. Relative cleaning efficiency in areal percentage cleaned, of five competing systems in cleaning heat exchanger tubes in Navy boilers. (Tursi, T.P. Jr., & Deleece, R.J. Jr, (1975) Development of Very High Pressure Waterjet for Cleaning Naval Boiler Tubes, Naval Ship Engineering Center, Philadelphia Division, Philadelphia, PA., 1975, pp. 18.)

Why such a difference? Consider how the power changes from the time that it first enters the pump motor, and then is converted into power along the line to the target. The numbers that I am going to use may seem extreme, but they actually mirror an early experimental set-up in our laboratory, before we learned better.

A water flow of 10 gallons a minute (gpm) at a pressure of 10,000 pounds per square inch (psi) pressure will contain – using the above equation;

10,000 x 10/1714 = 58.34 horsepower (hp)

But that is the power in the water. Pumps are not 100% efficient, and so there has to be some additional power put into the pump to allow for the relative efficiency of the pump itself. For the sake of illustration let us say that the pump converts the energy at 90% efficiency. Thus the power that is supplied to the drive shaft of the pump will need to be:

58.34/0.9 = 64.8 hp

But that is still not the power that we have to supply, since that power – usually – comes from an electric power cord that feeds into a motor, which then, in turn, drives the pump shaft. That motor itself is also not 100% efficient. Let us, for the sake of discussion, say that it is 92.6% efficient. Then the electrical power supplied will be:

64.8/0.926 = 70 hp

Now, as the calculation progresses, remember that this is the power that is being paid for. And so, in the first part of the flow, the power is transformed, from electric power to water power, but at the pump.

Change in Power from Motor to Pump

Figure 4. The change in power from that input to the motor, to that coming out of the pump.

The water coming out of the pump then flows through either a length of pipe, or high-pressure tubing until it comes to the tool that holds the nozzle. There are a number of different factors that change the flow conditions to the point that it leaves the nozzle. The most critical, and often overlooked, is the size of the hose/tubing that carries the water. Particularly as pumps get larger and more powerful, and the flow rates increase, it is important to ensure that the passage for the water is large enough so that it does not require too much pressure to overcome the friction acting against that flow. I have, myself, put an additional 10-ft length of tubing on a drilling lance, and seen the cutting pressure coming out the end fall from that which drilled a rock at 12 ft/minute to where it could not drill at all. (The pressure drop was around 200 psi per foot). I mentioned in that earlier post that a competitor, running at a pump pressure of 45,000 psi was losing35,000psi of that pressure, just to overcome friction in pushing the water down through a tube that was too narrow. As a result the water coming out of the nozzle had barely enough pressure (10,000 psi) to cut into the rock.

At the same time very few people pay a lot of attention to how their nozzle fits on the end of the feed line, or how well it is made. Think of this – you have just spent $200,000 on a system, and yet, because the nozzle is a disposable part, you look around for the cheapest source you can get. You don’t size it for a good fluid fit, nor do you check how well it is machined. And yet the entire performance of your system is controlled by that small item. The difference between a very good nozzle and a standard nozzle can give as much as a factor of 10 improvement on performance – but who checks. The one you use saved you $15 relative to what you would have paid if you had bought the competing product, what a bargain – right?

There are different ways in which pumps operate and produce the high-pressure flow. With a fixed size of orifice in the nozzle and with a given pressure drop along the feed line the pressure at the nozzle will be correspondingly reduced. So that if, for example, we use a 0.063 inch diameter nozzle then the chart you developed after generating the table will show that this will carry a flow of 9.84 gpm at 10,000 psi. But let us suppose that the hose loses 20 psi per foot of length, and that the hose is 200 ft long, then the pressure drop along the hose will be 20 x 200 = 4,000 psi.

Thus the pressure of the water coming out of the hose will be only 6,000 psi. And at an orifice of 0.063 inches, the flow through the orifice will now only be 7.62 gpm. (The way in which the pressure is controlled is assumed to be through bypassing extra flow back to the reservoir through a bleed-off circuit).

Now the pump is still putting out 10 gpm at 10,000 psi, but now the flow out of the nozzle is only 7.62 gpm at 6,000 psi. The power in this jet is (7.62 x 6,000/1714) only 26.7 hp. This is only 38% of the energy going into the pump.

Power from motor to nozzle

Figure 5. The power losses to the nozzle.

Unfortunately this is not the end of the losses. Particularly in cleaning operations there is a tendency for the operator to hold the nozzle at a comfortable distance from the target, so that the effect can be seen. But, as I will show in later posts, the jet pressure can fall rapidly as stand-off distance increases, particularly with a poor nozzle. A good range for a normal nozzle in a cleaning operation is about 125 nozzle diameters. So that at a diameter of 0.063 inches this range is less than 8 inches. Many people hold the nozzle at least a foot from the target.

If the nozzle is held about that far from the target the pressure will have fallen by perhaps 65%. The water thus reaches the target at around 2,000 psi. The flow rate is 7.62 gpm, and the actual horsepower of the water doing the work is 8.89 hp. This is 12.7% of the power that is being paid for through the meter. And the unfortunate problem is that no-one can tell, just by looking at the jet, what the pressure and flow rates are. So that often these losses go undetected, and folk merely complain about how the target material is more resistant today, not recognizing that they are throwing away 87% of the power that they are paying for.

Power from pump to nozzle

Figure 6. Power losses from the power cord to the target.

One of the objects of this series is to help reduce these losses, by avoiding those mistakes that those of us who started in the industry some 40-odd years ago made all the time.

Labels:hydraulic horsepower,line losses,nozzle losses,Pressure losses,pump losses,standoff distance

Waterjetting Technology-Adding Cracks to Nature

Waterjetting Technology – Adding cracks to Nature

In the last few weeks of the KMT Waterjet Weekly Blog Series, I have focused on demonstrating, with examples, that water effectively removes material by penetrating into natural cracks in the material and causing them to grow. But what happens when there are not enough cracks to remove material at an economic rate? The modern approach has been to raise the pressure of the water so that smaller cracks grow faster, thus providing the production rates needed, but that option wasn’t available in the past.

I mentioned last time that miners in the Caucasus Mountains of what is now Georgia used the power of mountain streams to erode gold deposits over 3,000 years ago. Perhaps learning from that, when the Romans came to Las Médulas in Spain, some 2,000 years ago, they though of water again as a way of mining the gold-bearing sandstone of the local hills. And though they had to modify the initial idea, the result became the most important gold mine in the Roman Empire. It is now a World Heritage Site.

Figure 1. Location of Las Médulas in Spain. (Google Earth)

Figure 1. Location of Las Médulas in Spain. (Google Earth)


The sandstone was more resistant than soil, and so the Romans came up with two ideas to improve the rate at which the gold ore could be removed. The first idea was to run galleries into the sides of the hills, creating large chambers underground, with support for the roof from wooden supports that were left in place.

Figure 2. Tunnel driven into the bottom of the hill at Las Médulas.

Figure 2. Tunnel driven into the bottom of the hill at Las Médulas.


Figure 3. Underground room at Las Médulas.

Figure 3. Underground room at Las Médulas.

At the same time that the mining preparations were going on local streams were being diverted and dammed so that a large volume of water was held in reservoirs and then carried by manmade channels to a point over the mining chambers. With the water ready, the timbers were set on fire, which initially weakened the overlying rock so that it began to fail, falling into the opening, and as the support burned away more rock fell into the opening until the cavity worked its way up to the surface. At this point the reservoir gate was opened and water flooded down the channel to fall into the cavity. As the water fell it further broke the rock into grain-sized pieces, and carried these down and out through the original opening in the hillside.

Figure 4. A Collapsed cavity, not the two figures at the arrows to get a sense of scale.

Figure 4. A Collapsed cavity, not the two figures at the arrows to get a sense of scale.

The water and debris flow was directed into flumes, in much the same way as modern miners in Alaska practice today, except that where carpet is used to catch the gold particles in Alaska, in Spain the Romans used plant stems (silex) to catch the gold. After drying the plant could be burned, easing to recovery of the gold. (In more modern times Spanish miners have lined the flumes with oxen hides.)

Figure 5. Artist sketch of the troughs used to capture the gold particles at the Spanish mines.

Figure 5. Artist sketch of the troughs used to capture the gold particles at the Spanish mines.


The use of heat to weaken rock before using water pressure for cutting has been tried with a couple of interesting wrinkles both by researchers at Rolla, and at the then U.S. Bureau of Mines and in Colorado, among others. But those more modern trials will be described later in the series. Using water streams to erode surface outcrops of mineral survived as “hushing” in the North of England and elsewhere until fairly recently.

Move forward some 1800 years or so from Roman Spain, and at the turn of the 19th Century miners in both Russia and New Zealand had a problem in mining coal. In both countries there were good quality coal seams, but they sloped at a steep angle that made it difficult to move men around without their slipping and falling. It was also difficult to support the roof, which was achieved at the time by sawing wooden props to length and wedging them between the roof and floor. Both nations had the idea of modifying the Roman idea of using water to remove the mined coal, but coal was thought to be somewhat stronger and more resistant than the Spanish sandstone.

In the New Zealand case the mountainous countryside makes it expensive to drive roads and as early as 1891 wooden flumes were being used to carry coal to the consumer. However it was then realized that the water could be used to also remove the mined coal, particularly that which was left in regions of the mine where it was not safe for men to go. The coal was therefore initially blasted, and then the flow from the nearby streams was directed at the debris pile. The volume of water, and the slope of the mine combined to remove all the mined coal, often overnight, so that a new area could be worked the following day. It was not until 1947 that pumps began to be used to drive the water at greater pressures. At this point, with the higher pressures that pumping brought, it was no longer necessary to pre-crack and break the coal with explosives.

While the New Zealand coal seams outcropped at the surface in very hilly ground, the situation was somewhat different in the Donets coal seams in the Soviet Union, where the seams were thinner, and production was barely economic. The seams in these mines were much deeper than in New Zealand, and so jet pressure could be provided from the drop in height from the mine surface to the location of the large nozzle or monitor that was used to aim the water flow at the coal. As with the New Zealand experience the Soviet miners (at the Tyrganskie-Uklony mine) initially blasted the coal with explosives to weaken it with a high density of cracks, before applying the water. However the miners found that not only did the water double production (to 600 tons/shift) the streams were powerful enough that it wasn’t necessary to pre-blast the coal. The nozzle diameters of the time were up to 2-inches in diameter, and could throw a jet up to 60 ft.

Figure 6. Early Soviet underground coal miner

Figure 6. Early Soviet underground coal miner

It was from these small beginnings that hydraulic mining began, it was, in its time the most productive method of mining gold in California, and was used for many years around the world for mining coal, and other minerals. But that again is a subject for more detailed discussion at a later time.

The combination of explosives and water power remains in use in harder rocks, particularly in South Africa in the gold mines. Here again the seams of gold are very narrow and can slope or dip at a steep grade, the working area is thus kept very cramped and difficult to work. By blasting the ore with explosive, it can again be moved with water pressure, although there is an additional advantage to water here that I will further explain when I write about cleaning rust from plates.

Gold, as is shown by the way it can be collected in flumes, is very heavy, and part of the problem in the South African mines is that small pieces can get trapped in small pockets on the floor of the seam. The higher pressure water flows can flush out these pockets driving the gold particles down to a common collection point. In that particular the practices haven’t changed that much in three thousand years.


Labels:Ancient Roman,coal mining,Donetsk,flumes,gold mining,hydraulic mining,New Zealand,Russia,Soviet Union,Spain