Misting System Lines & Fittings

Lines, fittings & connectors determine the position of each mist outlet, maintain water pressure, and help ensure leak-free, reliable, and effective outdoor area cooling.

What are Misting System Water Lines and Fittings?

Water lines are referred to by many names: pipes, tubes, hoses, cables, channels. These are all different names for the simple component that delivers the water from the supply source to the nozzles. The main considerations for the water lines are: size, style (flexible or rigid), material of construction, and water pressure rating.

• Size
• Style: flexible or rigid
• Material of construction
• Water pressure rating

Fittings, discussed later, describe a number of ways that sections of the lines are all connected.

Learn what makes a great misting system.

Misting System Line Size and and Wall Thickness

A misting system uses narrow water supply lines to maintain and deliver available water pressure. These supply lines are sized based on the diameter of the line. Most supply line material is measured “nominally”, which is an average diameter along the length of the line. The sizing used in misting systems is fairly standard. 3/8″ and 1/2″/ 9mm and 15mm diameters are the most commonly used. 3/8″/ 9mm is typically used for residential systems and commercial hospitality use. 1/2″/ 15mm is used for large industrial projects where much more water flow is needed. These standard sizes simplify connections to pumps and nozzles.

Thicker walled lines have greater durability and higher pressure tolerances as well as greater cost. Wall thickness does not affect line size (diameter). 1/2″/ 15mm L copper (thin-walled) has the same outer diameter as 1/2″/ 15mm K or M (medium- or thick-walled) copper. The same applies to plastic. The diameter stays the same on the outside, but the inside hole / channel gets smaller as the walls get thicker. As a result, water volume in the line decreases as wall thickness increases. When balanced with water pressure, water volume affects the “reach” of the spray – how far it travels from the nozzles. More volume means greater reach.

Misting Line Styles: Flexible or Rigid

Flexible lines can be very easy to work with and install. They need no special tools and allow for virtually any nozzle spacing — just cut the line wherever you want to place a nozzle. They can also be a perfect choice when setting up a misting system in hard-to-reach areas, or is situations where the tubes must make bends and turns. Flexible tubes also allow for flexibility in the overall design of the misting system because nozzle spacing can be decided on the spot, and because sections can easily be removed and re-configured.

Flexible materials may be made of various plastics or nylon and might or might not be reinforced with braiding. With any flexible tube, be careful not to bend it into too tight a curve. It can kink the tube and diminish or completely shut off the water flow. Flexible lines are available in stock lengths as short as 24 inches / 61 centimeters or as long as 500 feet / 152 meters. Some are treated to withstand outdoor exposure by being treated with a UV protective coating. Flexible lines cannot be painted, but are often available in more than one color to blend with the surroundings.

Rigid lines range from plastic, such as PVC to copper to stainless steel. Rigid lines make a neater looking installation and can be painted or powder coated to blend in to the surroundings. Rigid lines also stabilize the nozzles so origin of the spray remains constant. Rigid lines can be compression fitted like flexible lines, or solvent welded for long-lasting leak-free connections. Often a combination of flexible and rigid lines are used — flexible around obstructions and corners and rigid for a neat appearance where visible.

Misting Line Materials: Water Pressure Ratings

The selection of line material is based on water pressure and durability requirements. All are rated to withstand certain ranges of water pressures. Some of these can only be used with low pressure, but others can be used with medium or high pressure. Make sure all the components of your system are rated to work with your misting system’s water pressure. Some must be painted or treated with a UV coating to protect them to long-term outdoor exposure.

Following are some materials that are commonly used for misting system lines.

Plastic / Thermoplastic – Schedule 40 is rated to 300 psi / 20 bar; Schedule 80 is rated to 500 psi / 34 bar.

Compared to other materials, plastic is lightweight, easy to work with, and costs considerably less but is only suited to low- and mid-pressure systems. Plastic lines, especially flexible lines, are great for a portable misting system because of their light weight.

Schedule 40 in 3/8-inch and 1/2-inch outside dimensions are used for low- and mid-pressure systems. The smallest dimension for Schedule 80 is 1/2-inch, which is suitable for the higher flow rates of larger systems. Some plastics can be joined with solvent fittings, other can use push-in fittings or compression fittings. Here are the most popular:

• PVC (polyvinyl chloride) Rigid and PE (polyethylene) Flexible lines are ideal for low-pressure misting systems. PE lines cannot be solvent welded. Both are low-cost, can be found easily at a local home improvement store, and are easy to install. They will not rust or corrode; and have insulation qualities that prevent condensation from forming on pipes carrying cold water.
• CPVC (chlorinated polyvinyl chloride) Rigid is another rigid plastic used for low water pressure systems. It will last a long time, though is not quite as tough as copper. It should be painted or covered for long-term outdoor use.

PVC, PE, and CPVC are available in different wall thicknesses called “Schedules”. The most commonly used wall thicknesses for a misting system are Schedule 40 (rated at about 300 psi / 20 bar), and Schedule 80 (rated at about 500 psi / 34 bar). These are resistant to UV radiation, but prolonged exposure can decrease their impact strength and resistance.

According to PVC fittings online, to ensure PVC and CPVC lines and connectors are protected from long-term UV exposure, paint them with acrylic-based latex paint or cover them when not in use.

• Solvent fitting is typically used for plastic / thermoplastic lines. It uses a solvent matched to work with the specific type of plastic used for the line. The solvent is applied to the outside of the line end and the inside of the connector, and the two pieces are joined together while the solvent has temporarily dissolved the plastic of both pieces. When the plastic re-hardens, the two pieces will have been permanently “melted” into a single water-tight unit. These fittings can be more water-tight and durable than compression fittings. Some plastics, like the flexible PE lines cannot be solvent welded and must be compression welded.

• Generally not recommended: PEX is commonly used for indoor plumbing because it is flexible and can be installed with fewer connectors than rigid plumbing systems. While PEX is generally durable up to 160 psi, PEX-A can withstand up to 500 psi. But these are likely to breakdown within a matter of only a few months when exposed to direct sunlight. Be prepared to replace these lines according to their UV exposure ratings: 3 = replace every 6 months, 2 = replace every 3 months, 1 = replace every month, 0 = not recommended for outdoor use. If you have some lying around that you want to use for a month or a season, or for a temporary repair, use it only where it will be well-protected from sunlight, such as under the eaves of a solid patio cover.

Nylon – Typically rated up to 1000 psi / 70 bar

• Flexible virgin nylon is newly manufactured and is much stronger that recycled nylon. Often UV protected, virgin nylon will withstand the most demanding outdoor conditions. Often used to route high pressure water from pump to copper or stainless steel mist lines, this flexible line can be directly clamped down or fished through conduit in a structure, in the ground, or under concrete. Like other flexible lines, nylon can be fitted with simple push-in fittings or compression fittings. Nylon is available in cut lengths, or in rolls from 100 to 1000 feet / 30 to 300 meters. 1/4-inch and 3/8-inch outside dimensions are the most commonly used. The larger dimensions will handle higher flow rates, suitable for a larger number of nozzles and for larger spray.

Synflex – rated up to 1500 psi / 103 bar

Synflex uses a nylon core surrounded by a synthetic fiber, which is coated with polyurethane to create a flexible, durable, lightweight line. 1/4-inch interior dimension is commonly used and will handle up to 3 GPM flow rate. 3/8-inch is also available.

Copper – Type L is used for misting systems and is rated about 1000 psi / 70 bar

Rigid and flexible copper lines are available. Rigid copper makes a neater installation for your misting system, but is much more difficult to install than flexible copper. it cannot be bent and must use elbow fittings to go around corners or obstacles. Flexible copper line is good for running around obstacles without connections or cuts. It can be joined by several methods, and is the only type of copper line suitable for flare connections. Pre-fabricated copper line is designed for quality and versatility and is a good choice when rigid lines and on-the-job customization are required.

Copper is available in stock lengths of 10 or 20 feet / 3 or 6 meters, and is also available in custom lengths. Copper is highly resistant to corrosion, but is becoming very costly. Copper line is available with three wall thicknesses: Type L – medium-walled is typically used for misting systems. Type M is thin-walled and Type K is thick-walled.

Copper should not be used if the water has a PH of 6.5 or less. Most public utilities supply water at a PH between 7.2 and 8.0 but private well water systems often have a PH below 6.5. When this it the case, installing a treatment system to make the water less acidic can prevent damage to these lines.

Stainless Steel – rated to 3000 PSI / 207 bar

Rigid stainless steel lines are the ultimate for quality and durability and can handle the higher pressures of large, commercial misting systems. These lines can be powder coated and painted to match the surroundings.

Fittings and Connectors for Misting Systems

A fitting isn’t necessarily a physical piece of plumbing, but is a general term to describe any of a number of ways that sections of line are “fitted” or joined together. Fittings link together individual sections of the line, link the line to the water supply or pump, and link the line to the nozzles. Typical methods of fitting used for misting systems are:

• Compression fittings “screw” on with spiraling “threads” which are shaped at the ends of most water lines. These are perfect for the do-it-yourselfer. Compression fittings commonly have an outer compression “nut” or connector, and a “ferrule” or disk (also called an “olive” in the UK) that fits between the nut and the line. When the nut is tightened, it clamps down on the ferrule, forcing it to conform to the shape of the line and eliminating all space in the joint.

Over-tightening is the most common cause of leaks in compression fittings. If the fitting is over-tightened, the ferrule will deform and cause leaks. As a general rule, a compression fitting should be hand tightened.

Compression fittings are easy to use and require no special tools or skills to put together, yet still provide water-tight seals that can withstand the pressures of a misting system. Compression fittings are especially useful when occasional disassembly or partial removal is needed, such as in temporary installation, since these joints can be disassembled and remade without affecting the integrity of the joint. Compression fittings are a good choice in confined spaces where soldering would be difficult or dangerous. But they are not as durable as soldered fittings, and should not be used where the fitting will be subjected to repeated flexing or bending.

Make sure compression fittings for all connections are properly rated. Secure all these fittings with plumbing tape to reduce the chance of leaks. Check that all fittings are properly tightened.

Some compression fittings use “push-to-connect” or “slip-to-lock” hardware, which combine the compression nut and ferrule into one piece. They are simply pushed onto the line to form the connection. These are quicker and easier to install than standard compression fittings, but may be more likely to leak.

• Sweat fitting is a way to join copper tubing using “solder” (a fusible metal alloy) like a metal “glue”. A sweat fitting is a smooth disk that easily slips onto the end of a section of the water supply line. The joint is then heated using a torch and solder is melted into the connection. When the solder cools, it forms a very strong bond which can last for years. With experience, sweat connections are quick to create, and when many connections must be made at once, sweat fittings can be quicker to join than compression or flare.

• Crimped or pressed connections use special copper fittings which are permanently attached to rigid copper lines with a powered crimping tool. The special fittings, manufactured with sealant already inside, slide over the tubing to be connected. Thousands of pounds-force per square inch of pressure are used to deform the fitting and compress the sealant against the inner copper tubing, creating a water tight seal. The advantages of this method are that it should last as long as the lines, themselves, it takes less time to complete than other methods, it is cleaner in both appearance and the materials used to make the connection, and no open flame is used during the connection process. The disadvantages are that the fittings used are harder to find and cost more than sweat type fittings.

• Flare fittings spread the end of a line section be outward into a bell shape using a flare tool. Then a special “nut” compresses this bell-shaped end onto the next section of line. Flare connections are very durable and can remain water-tight for many years. But they are labor intensive and can be used with only a few misting line materials.

We have some surprising tips on what to look for and how to shop for a system in Selecting a Misting System.