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The Spray Nozzle In Action

The spray nozzleis an important component of the high pressure cleaner in that it is the point at which the cleaner interfaces directly with the work being accomplished. Because of its importance, it is critical that the right nozzle of the correct sizes be used and that the nozzle be properly cared for.

The Spray Nozzle Orifice

Both the size of the spray nozzle orifice or outlet and its shape affect the amount and type of cleaning work water directed through the nozzle will be able to accomplish.

Orifice diameter (the diameter of the hole in the discharge side of the nozzle) determines the pressure produced at a particular flow. A smaller orifice will produce a higher pressure or psi figure at a specific flow or gpm than a larger orifice. Pressure represents the amount of force needed to move water through the nozzle orifice.

The shape of the nozzle outlet determines the spray pattern, which is generally either straight stream or fan spray. The more concentrated or narrower the spray pattern, the less surface will be covered but with more impact of water against the surface. Fan jet patterns of 14, 25 and 40 degrees are common.

The Difference Size Makes

To see the difference orifice diameter makes in flow and pressure, compare a 6.5 and a 4.0 spray nozzle. At a flow in the vicinity of 2 gpm (really 2.1) the 6.5 spray nozzle produces a pressure of 400 psi. The 4.0 spray nozzle, however, produces 1000 psi at a 2 gpm flow.

The higher the flow and pressure, the more impact and cleaning power – with certain qualifications. For example: hot water at higher pressures - 3,000 psi and above – may lose some cleaning power through vaporization and dissipation.

Sizing Spray Nozzles

Spray nozzles are sized to produce the equipment’s rated flow and pressure. Spray nozzle sizing for most pressure and flow ratings are included in the spray nozzle chart. This chart is easy to read Look at the top of the chart where there are captions for columns representing pressures from 500 to 3000 psi. Spray nozzle sizes are assigned to each line. The flow rate produced by that spray nozzle size at the psi is entered in each column on a line.

To find the correct spray nozzle size, look up the psi rating of the machine in the line of captions at the top of the page. Run your finger down the column till you get to the closest entry to the flow produced by the machine.

If you do not have the exact size when replacing a spray nozzle, use the next size larger rather than a smaller because moving water through the smaller orifice will require more effort from the electric motor and consequently more amperage. The increased draw can trip a circuit breaker. This can be a particularly annoying problem with 115 V hot water machines, which usually operate on circuits with 20 amp breakers and normally draw 17 to 19 amps for operation.

Nozzle orifice dimensions are given for a round hole of equivalent area to the actual elliptical opening and are measured in hundredths and thousandths of an inch. Nozzle sizes are generally expressed as a whole number rather than a fraction. The whole number is not necessarily an expression of the actual equivalent diameter. In other words a 65 or 065 nozzle under the most accepted system has an equivalent diameter of .060 inch. A 4 or 040 nozzle has an equivalent diameter of .047 inch.

The nomenclature is somewhat confusing. Historically, the basis of nozzle sizing is the "four, four, four rule." Simply, the rule states that a 40 nozzle at 4 gpm will produce 4000 psi. "As nozzle orifice apertures increase in size the system comes back around and a 10 nozzle has a .075 equivalent aperture diameter. A 20 nozzle could have an aperture of either .106 (large) or .36 (small)and a 40 could be 0.150 or .047."

In technical literature the smaller orifices are designated with a preceding zero but when nozzle sizes are discussed it is generally assumed that a reference to a "40 nozzle" is a reference to a smaller equivalent diameter.

To make it even more befuddling, different manufacturers may use slightly different sizing systems. One manufacturer rounds off equivalent diameters to the nearest hundredth of an inch, and, consequently lists three different sets of flow and pressure characteristics for nozzles of the same apparent equivalent diameter.

Thus, nozzle sizes based on specifications alone will show discrepancies. One of the most popular pressure washers today is a 22 gpm, 1000 psi machine. However, you will discover, when checking standard nozzle sizes, using nozzle charts prepared by the leading United States nozzle manufacturer, that one size produces 1000 psi at 2 gpm and the next larger size produces 1000 psi at 2.3 gpm. The same is true of many other standard sizes. (A comparison of nozzle charts prepared by different nozzle manufacturers shows a number of differences in rated flow and pressure for nozzles of the same apparent size. We have relied on the Spraying Systems specifications for their popular Washjet nozzle.)

Factors Affecting Spray Nozzle Sizing

Components in the system may also affect nozzle sizing decisions when the proper nozzle size is not available. Here is how:
Open gun or dump gun. The next larger size spray nozzle should be used to help prevent over pressurization of the system.
Pressure unloader. The next smaller size spray nozzle should be used because the pressure unloader will automatically bypass any excess flow. The rated system pressure will be maintained but flow will be reduced slightly.
Flow unloader. The next larger size spray nozzle should be used. Use of the larger size spray nozzle may cause a slight loss of pressure but will guarantee that all flow is passed through the nozzle. A spray nozzle orifice that is too small will cause the flow unloader valve to cycle under pressure. If the unloader type is not know, use the next larger size.

Flow and Pressure Differences

To illustrate the difference that the orifice diameter makes in flow and pressure, let’s compare a 65 and a 40 nozzle. At a flow in the vicinity of 2 gpm (really 2.1) the 65 nozzle produces a pressure of 400 psi. The 40 nozzle, however, produces 1000 psi at a 2 gpm flow.

The higher the flow and pressure the more impact and cleaning power-with certain qualifications. For example: hot water at high pressures-3000 psi and above-may lose cleaning power through vaporization and dissipation.

Arguments continue in the industry over whether flow or pressure is more important. One side argues that a higher pressure will produce better cleaning results while the other maintains that after a certain pressure is reached; improved results can best be obtained by increasing flow.

The Right Spray Angle Is Important

The nozzle’s spray angle also helps determine the cleaning ability of a specific flow at a specific pressure. The angle refers to the theoretical spread in degrees of the stream of water coming from the nozzle or the angle or shape of the spray pattern.

Spray nozzles used in pressure cleaning generally range from zero degrees to 65 degrees in theoretical spray pattern spread. These spray patterns are available in only a few predetermined spray angles. The narrower the stream of water coming out of the nozzle, the more impact, but the less coverage and the longer it might take to clan a specific area.

The most popular nozzle is the 25 degree nozzle, which is considered to represent the best compromise between spray pattern coverage and impact.

Some experienced operators prefer a 15 degree nozzle, trading off greater impact for less coverage and making up for reduced coverage with skill in using the equipment. When a machine comes with more than one nozzle the patterns are generally zero degree, 25 degree and 40 degree. The wider-angle nozzles are generally used for detergent application or rinses.

Distance From The Surface Being Cleaned

How far the spray nozzle is from the surface being cleaned makes a major difference in water impact. The greater this distance, the less impact water will have. However, the greater distance increases the amount of area covered by the spray. The operator can easily adjust the spraying distance to suit different types of cleaning applications and perform his job most efficiently.

When water is sprayed into the atmosphere from the nozzle it immediately begins losing speed, and consequently force, due to air friction and other factors. Holding the spray nozzle very close to the surface will give more impact on hard-to-clean areas.

Holding the spray nozzle four or five inches away will be adequate for most moderate soils. (The wider the spray pattern, the closer the nozzle will have to be held to the surface to get the same performance as a nozzle with the tight, 15 degree spray pattern.) The larger the equipment’s output, the greater the distance the water spray is capable of traveling while still retaining adequate cleaning ability.

The Right Spray Angle For The Job

Most pressure cleaning nozzles are of the fan spray or flat spray or flat spray type. The most popular nozzle pattern is generally agreed to be the 25 degree nozzle, which is considered to represent the best compromise between spray pattern coverage and impact. Some experienced operators prefer a 15 degree nozzle, trading off greater impact for less coverage and making up for reduced coverage with skill in using the equipment.

The different spray patterns have different characteristics and are useful for different types of jobs. Here are some of the benefits of each of the standard spray patterns.
Zero degree - (also known as pencil jet) maximum impact but minimum coverage. The spray pattern is circular and coverage area is small. Good for cleaning tight areas and the very heaviest, most stubborn soils.
15 degree – spray pattern is tight enough for significant impact at six inches or less. Pattern is wide enough for fair coverage at 12 inches or more. Good for cleaning heavy to moderately heavy soils. A skilled operator can use a 15 degree spray nozzle for efficient, general duty cleaning.
40 degree – wide coverage but reduced impact. Good for light duty cleaning and general rinsing.

Theoretical Spread and Spray Angle Coverage

Although nozzle spray patterns are expressed in degrees of spread, these figures are not precisely accurate as the distance between the cleaning surface and the nozzle increases, which is why the terms theoretical spread or theoretical coverage are used. Theoretical spray angles indicate approximate spray coverage’s based on water velocity. In actual use the spray angle varies with distance.

Formulas for Common Nozzles

The theoretical coverage (fan width) for distances other than those given in the table above can be calculated from these formulas:

There are two types of fan
or flat spray nozzles, elliptical orifice or a round orifice set at an angle to a deflecting surface. The elliptical design is by far the most common in the pressure cleaning industry. It produces a spray pattern with tapering edges. Wider droplet dispersion over the surface area is found at the edges of the spray pattern. This works best when the operator sprays in overlapping patterns, making the overall spray more uniform. The deflector type, on the other hand, produces a spray with even edges and may be used in cleaning applications, which require uniform impact over the pattern width without overlapping.

Using the right nozzle – the one that suits both your operator and the application, is most important for achieving good results from a pressure cleaning operation.

Releasing Stored Energy

The spray nozzle forces water to perform work. Water is essentially incompressible. That means the water flowing through the cleaning system form the pump is not really pressurized or compressed like a gas would be. Instead, it is simply moving throughout the system at a rate of flow generally expressed in gallons per minute or gpm.

The pressure nozzle restricts the flow and increases the water’s velocity and potential for impact on the surface to be cleaned. In fact, you could say that the cleaning machine’s pressure is first manifested at the spray nozzle restriction. The potential energy created by the pump and "stored" in the water moving through the system becomes kinetic energy – that does work – when it escapes from the spray nozzle.

The spray nozzle restricts the water flow out of the system. The spray nozzle also directs the water in a spray pattern, usually V – or fan-shaped. Orifice diameter determines the pressure produced at a particular flow. A smaller orifice will produce a higher pressure or psi figure at a specific flow or gpm than a larger orifice.

How Most Spray Nozzles Are Manufactured

Fan spray nozzle orifices are generally elliptical rather than round. This is the result of the method of manufacture. Fan spray nozzles are made from blanks that are pretty much already machined to their final shape.

A round hole is then drilled through the blank from the back and a cut is made across the front. This is called drilling and milling and the result is a three dimensional elliptical opening. The drilling process determines the spray orifice size. The milling cut determines the spray angle. Most – but not all – spray nozzles used in the industry are machined in this manner.

Spray Nozzle Orifice Dimensions

Spray nozzle orifice dimensions are given for a round hole of equivalent area to the actual elliptical opening and are measured in hundredths and thousandths of an inch. Spray nozzles are generally expressed as a whole number rather than a fraction. And the whole number is not necessarily an expression of the actual equivalent diameter. A 6.5 or 065-spray nozzle, under the most accepted system, has an equivalent diameter of .060 inch. A 4.0 or 040 spray nozzle has an equivalent diameter of .047 inch.

Material and Wear

Pressure washer nozzles are generally made of steel, often hardened stainless steel, although some new, high-pressure nozzles are made with tungsten carbide inserts to lengthen nozzle life. Some nozzles used in the industry are made of ceramic, which is very resistant to wear but is easily shattered.

Wear on the nozzle will eventually result in pressure loss as the flow of water slowly enlarges the orifice. In a fan spray type pattern, the most common in the industry, a narrowing of the spray pattern will also be noticed. Because of the variety of variables such as type of chemicals used, hardness of the water and the velocity of the spray, to name three, engineers are reluctant to give estimates on nozzle life.

Additionally, the amount of wear permissible varies according to application and user preferences. That is, will a slight but steadily increasing pressure loss over time make enough of a difference to necessitate a nozzle change and at what point in the wear pattern should this change be made?

The answer is up to the operator. However, a nozzle change, rather than an unloader adjustment, is the first action to take to correct such a pressure loss. In general, nozzles are precision tools designed to perform specific tasks. If used properly and treated with respect, even the more complicated and delicate accessory nozzles will provide a good service life.

Quick Connects For Easy Nozzle Changes

One good way to extend nozzle life is to attach all nozzles, and especially specialty nozzles such as rotary nozzles, to quick connects to that they can be removed for proper storage when no in use. However, this increases the possibility of the nozzles being lost when no in use.

It should be stressed to operators that spray nozzles are precision tools, which can be interchanged easily but should be handled with care just like any other precision tool.

Whenever a quick connect is used to make a spray nozzle change, check to see that the locking ring has snapped back to the locked position. If the ring has not returned to the locked position, the spray nozzle will be shot out of the lance by water pressure as soon as the trigger is depressed.

Clogged Nozzles

Nozzle clogging is one of the most common nozzle problems. Clogging results either when debris works its way through the system to the nozzle or when debris is picked up from external sources by the nozzle when there is no water flow through the lance.

A distorted or broken spray pattern, sometimes coupled with low or erratic pressure, is a sign of nozzle clogging. A clogged nozzle may cause problems, which may initially be diagnosed as a problem elsewhere in the system. A clogged nozzle may be initially diagnosed by the operator, as a pump or unloader problem, for example.

Preventing Clogging

The best way to prevent nozzle clogging from internal debris is to always start with system either without a nozzle or with a variable pressure lance set to the lowest possible pressure. Debris, which could clog the high-pressure nozzle, may be flushed out through the end of the lance or through the low-pressure nozzle’s substantially larger orifice.

Debris From The Water Supply

Clogging from debris passing through the system from the water supply is rarer than from other causes since there are so many intervening areas where such debris can lodge. Another debris-related problem, such as a stuck check valve, is likely to occur before nozzle clogging results from debris entering the system at the water supply.

Debris in the water supply is most often picked up when the discharge hose is disconnected from the cleaner for storage. The hose is usually dropped to the ground, where it is likely to pick up debris, before it is coiled for storage. Debris may also originate inside the machine. Debris may result from deterioration of seals or other polymers or from internal rust or corrosion as well.

Remove Nozzle For Cleaning

If a spray nozzle is clogged, it is best to remove it from the lance before cleaning it. Cleaning it from the outlet end will simply push the debris back into the system and re-clogging may result. Removal of the spray nozzle while it is still clogged will usually guarantee that the trapped debris is also removed.

Once the nozzle is removed from the system, a probe of suitable size may be used to push the debris out of the nozzle. This should be done from the outside in. Any debris remaining in the inlet side of the nozzle should be cleaned out. If time or chemical scale is present in the inlet side, the nozzle may be soaked in decaling solution or replaced. Scale will form on the inlet side of the nozzle and may create problems elsewhere in the system long before the orifice is restricted by scale. Before replacing a cleared nozzle, flush the system thoroughly with the nozzle removed to clear any additional debris from the system.

Orifice Diameter

Orifice diameter determines the pressure produced at a particular flow. A smaller orifice will produce a high pressure or psi figure at a specific flow or gpm than a larger orifice. Fan spray nozzle orifices are generally elliptical rather than round.

This is the result of the method of manufacture. Fan spray nozzles are made from blanks that are pretty much already machined to their final shape. A round hole is then drilled through the blank from the back and a cut is made across the front. This is called drilling and milling and the result is a three dimensional elliptical opening. The milling cut determines the spray angle.

Non-Standard Spray Patterns

The flat or fan spray pattern is the most common in high-pressure cleaning systems, but other patterns such as hollow cone and solid cone are available as well. These spray nozzle types are generally designed for use at lower pressure than is normally the case in pressure cleaning applications. However, most nozzles can be used at a higher pressure than they are rated although such use is not recommended by manufacturers and may eventually cause problems. Using a low-pressure nozzle type at higher pressure will probably deliver less than optimum performance and should be avoided.

Nozzle Protectors

Most nozzle wear is due to external abuse. Concrete is probably the great nozzle killer. Equipment operators will bang the nozzle against the concrete, drag it across concrete or even use the lance and gun nozzle down as a crutch or cane. It’s very easy for the operator to develop a habit of leaning on the gun and lance when taking a break. Not only will this wear down the nozzle, resulting in spray pattern deterioration, the nozzle can easily become clogged.

Nozzle protectors are available. Usually made of rubber, these devices should extend past the nozzle a little and can prolong nozzle life. The protectors, however, will have to be replaced on a regular basis.

Other Nozzle Types

Nozzles that allow variable patterns, often with three or four different nozzle tips set to rotate into position, are available for lower pressure-generally no more than 1000 psi. In order to increase impact, some nozzles are made to create oscillating or intermittent flows with a turbine or cam arrangement.

However, most nozzles can be used at a higher pressure than they are rated for, although such use is not recommended by manufacturers and may cause problems.

Besides the standard spray nozzles used in most equipment, a number of other nozzle types may be employed in high pressure cleaning systems.

Rotating Nozzles

Rotating nozzles use one or two zero-degree nozzles, which are spun rapidly with water propulsion. These nozzles can increase the ability of a washer to knock off dirt at lower pressures than would normally be the case.

The single rotating zero-degree nozzle generally produces a conical pattern. Impact is high and the rotation greatly increases the area covered. When two zero-degree nozzles are used, the spray pattern is more cylindrical. However, each nozzle has only half the flow of a single nozzle with the same pump output.

Rotating nozzles, especially the less expensive ones, may have short operating lives. Temperatures over 160 degrees are generally not recommended although some rotating nozzles are rated for significantly higher temperatures.

At least one make uses a ceramic insert to reduce wear but this insert may shatter. Shattering can result if the nozzle is dropped or strikes a hard surface sharply. In general, rotating nozzles will not work well with very hot water and usually have a top temperature limit of 165 to 180 degrees Fahrenheit. Most rotating nozzles, especially the more expensive ones, are rebuildable. This generally involves replacement of seals. Gear assemblies and ceramic nozzle inserts may be replaceable as well.

Adjustable Nozzles

Adjustable nozzles are available which allow variable pressure or variable spray pattern adjusted at the nozzle. Instead of several standard nozzles on a rotating mount, the true adjustable nozzle is designed with moving parts, which allow orifice restriction or enlargement to change output pressure or variable spray deflection to change the nozzle spray pattern. Some adjustable nozzles are designed for both adjustable pressure and spray pattern.

Since these nozzles have moving parts, they are more expensive and more subject to wear than standard nozzles. Adjustable nozzles are usually supplied with equipment producing volumes and pressures in the lower ranges. For example, many hobby and small cold-water machines come with an adjustable nozzle to allow for low-pressure chemical injection.

Turret Nozzles

Multiple nozzle holders that allow variable patterns, often with three or four different nozzle tips set to rotate into position, are available for lower pressures generally no more than 1000 psi. These fittings, often called turret nozzles, allow the operator to switch quickly from one spray angle to another to suit the cleaning job being performed.

Generally a turret nozzle will have a zero, a 15 or 25 and a 40-degree nozzle. Some may have a 60-degree nozzle or a nozzle with a larger orifice for low-pressure chemical injection. These nozzles are most common on less expensive cold-water units.

The turret spray nozzle hold may be subject to wear and leaking, especially when used at higher pressures. Some spray nozzle holders hold only two nozzles, one for high-pressure and one for low-pressure chemical injection. These fittings are sometimes called rollover valves. Turret nozzle designs are subject to wear and may not withstand higher pressures.

Steam Cleaners And Vapor Expansion Nozzles

Steam cleaners use a nozzle type different from that used on high-pressure cleaners. When a combination cleaner is used in steam mode, the high-pressure nozzle should be replaced with a steam nozzle for effective cleaning. Steam nozzles work on the principle of vapor expansion rather than restriction of flow as do high-pressure nozzles.

Pressure, Liquids And Vapors

Pressure affects the point at which water boils or vaporizes into steam. At sea level water boils at 212 degrees Fahrenheit. At higher pressure water boils at higher temperatures. At any pressure over 80 psi water will remain liquid when heated to 325 degrees Fahrenheit, 113 degrees above the boiling point of water at sea level. Because the water is under pressure, it remains liquid at the 325-degree temperature, rather than vaporizing or turning to steam.

How The Steam Nozzle Works

Steam takes up much more space than water. When the superheated water in the steam cleaner suddenly drops to atmospheric pressure on passing through the nozzle, a percentage of the water volume turns to steam. And the steam expands.

A steam nozzle is designed to channel this vapor expansion to propel the water, which has not been vaporized against the surface to be cleaned. It begins with a pressure orifice much like a spraying nozzle. However, the nozzle ends several inches beyond this point, allowing a restricted area where vapor can expand. This vapor expansion propels water droplets out of the end of the expansion nozzle at speeds, which may exceed the speed of sound.

What happens in the steam nozzle is nothing more or less than a controlled steam explosion. The greater the distance the water travels from the end of the expansion nozzle, the more velocity and temperature it loses. Air friction slows the steam explosion propelled water droplets. As the droplets move through the air they cool, radiating heat off into the atmosphere. Consequently, the closer the nozzle is held to the surface being cleaned, the greater the impact and the higher the temperature.

Moleing Or Pipe Cleaning Nozzles

The pipe cleaning or moleing nozzle is very popular with the food processing and manufacturing industries. This nozzle design has one penetrating stream pointing forward and two or three orifices pointing backward to flush debris and prevent pipe clogging as well as to; push the nozzle forward. This type of device is especially effective when used with hot water to fight grease buildup in drainpipes or grease traps.

A trigger gun should be used with this nozzle type. The outlet hose should be fitted with the gun just as in a spray lance were being used. The pipe cleaning nozzle’s hose should then be connected to the gun. This gives the operator the opportunity to stop operation if the hose and nozzle should fly backwards out of the pipe.

Fixed Sewer Nozzles

The reverse jets on the fixed and rotary nozzles pull the hose through the tube or sewer line and blast debris from line or tube walls. Fixed nozzles also have forward orifice to blast blockage out of the way. The Sewer Nozzle slides easily into sewer or drain lines to flush debris and clean frozen pipes. Forward port blasts into pipe to break up clog and debris. Backward ports drive the nozzle forward while flushing debris.