THE 3 PARTS OF A MISTING SYSTEM

part 1: The Misting Pump

If you'd like to put together your own misting system, expand one you already have, or would simply like to understand the inner workings of a misting system, a misting pump is an important part of all systems.

It can help to understand the workings of a misting system by realizing there are 3 basic components:

• the misting pump, which we talk about here
• the lines & connectors
• the nozzles

We've devoted a separate page to each component.

The Misting Pump Supplies the Water Pressure

"Pump" is a simplified term for the pump and the motor combination.

The misting pump creates the amount of water flow (volume of water). The motor creates the pressure. The pump (and motor) are housed in a single unit that controls water volume and water pressure.

The water in your misting system needs enough pressure behind it to force it through the tiny nozzles that create the mist. You can get a sense of why that by observing your bathroom shower. When you turn the water on low (low pressure), the water just dribbles through the small holes of the shower head. But when you turn the water on high (high pressure), the water shoots through the holes, creating a fine spray.

A low pressure misting system works with typical cold water pressures and continuous water flow such as those provided by most water utilities. These pressures are based on the pull of gravity and can vary from 20 - 120 psi / 1 - 8 bar (about 60 psi / 4 bar is average).

Pumps are used to raise existing water pressure. They may be low pressure misting pumps, called "booster" pumps that raise the pressure to only 160 psi / 11 bar. There is little difference between these booster pumps and medium pressure misting pumps that raise the pressure up to 250 psi / 17 bar. But there is a greater difference between these and high pressure misting pumps that can raise the pressure up to 1000 psi / 70 bar and more.

The water pressure for reservoir, or tank fed systems such as portable units, is completely supplied by the pump. This is because the water source is usually so close to the nozzles that gravity has no chance to build up any significant water pressure. Since these systems have a limited amount of water available at any one time, they allow control of water temperature (the water can be chilled -- great for more humid areas) and composition (water can come from any reliable source).

Lower pressure systems use more water volume;
Higher pressure systems use less water volume.

The Setup Can Affect the Water Pressure

Most misting systems spray water from overhead which is likely to reduce water pressure somewhat because the water must travel "uphill" to get overhead. The more vertical distance it must travel, say, to high ceilings or upper level balconies, the more loss of water pressure is likely. The pressure also drops a bit for each time the water must turn a corner (supply lines making a right angle to turn around the corner of a structure), and a small drop in pressure for each nozzle in the system.

These pressure and flow drops are minimal per turn or nozzle, and may not be noticeable in higher pressure sytems. But low and medium pressure misting systems may suffer from small drops like these. In that case even low pressure systems may need a misting pump to maintain useable water pressure and flow.

Power Supply to the Pump

Misting pumps discussed here run on alternating current electricity, such as supplied by an electric utility company. Most misting systems run in the range of 110 volts or in the range of 220 volts and use a frequency of 50 or 60 hertz. Make sure the pump's voltages and frequency are compatible with your electricity supply.

A misting pump may withdraw large amounts of electricity (amps), but how those amps are used shows how much power the unit really has. The number of watts used will tell you and will also help you estimate operating costs.

Your pump must include a GFCI feature to shut off the electricity and prevent electric shock. Also, your misting pump, whether permanent or portable, should be rated to work in the conditions where it will be used. See our page on electrical safety outdoors for more information.

Types of Misting Pumps

Thousands of pump designs have been built for thousands of uses. Fortunately, established suppliers understand the features best suited to a misting system. The result is that some of these pumps have been standardized for economy and availability, while others are customized and specific to your application. Customized pumps might be pre-assembled pump systems, aggregates, modular units, fabricated systems or multiple pump systems, to name just a few. They can also be customized by power source - you might need a system powered by a hydraulic motor, a gas or diesel engine for portability, battery powered or solar powered.

You can work with a well-chosen supplier to determine what kind of pump you need and if you need a custom pump in the first place. Not all suppliers handle custom pumps though, so understanding your outdoor cooling needs will help you decide what's best for you.

The following types of pumps are the ones you're most likely to find for misting systems:

Centrifugal Pumps are efficient misting pumps with few moving parts requiring minimal maintenance and service. The flow rates from these pumps will vary depending on the amount of water pressure they create -- the more pressure the more flow.

Positive Displacement Pumps can be divided into two main categories: reciprocating or rotary. These types of pumps are mostly used for large volume, Low and Medium pressure systems. A reciprocating, positive displacement pump can be 40-50% more efficient and electricity costs can be 2-3 times less than a pulley driven pump.These misting pumps can be noisy, but some of these require virtually no maintenance. These motors are best for light duty use where price is the primary consideration.

Direct-Drive Pumps are especially compact and suited to portable, low demand misting. They use less electricity and need less maintenance than Pulley Driven pumps. But they are not as durable and do not have the added shock absorption of the pulley / belt drive pumps. These are the most economical of High pressure pumps and are also suitable for Low and Medium pressure systems.

Pulley / Belt Driven Pumps use a system of pulleys and belts. Pulleys provide the greatest flexibility in meeting a particular flow requirement. Belts provide added shock absorption during stops and starts. These are suitable for all systems when quality, versatility, and safe, convenient operation are the primary considerations. Pulley-driven misting pumps offer quiet, efficient operation. Some of these can be run 24 /7 even under extreme conditions. This kind of pump is top of the line but may require additional selection, installation and maintenance steps.

Is Noise Level a Concern?

Bottom threshold of human hearing	10dB
Recording studio	20dB
Quiet living room	30dB
Quiet office or library, refrigerator	40dB
Quiet conversation	50dB
Average office noise, clothes dryer	60dB
Average conversation, dishwasher	70dB
Average factory	80dB
Typical home stereo volume	90dB
Heavy truck	100dB

Pumps can be very noisy. Not only can the noise interfere with the comfortable environment you are trying to create, there may also be noise restrictions for the area where you want to use your misting system. Check with your local authorities about these restrictions before you purchase your misting system. Even though a manufacturer may describe the pump as operating "quietly", that can still be as noisy as a central air conditioning unit . . . which may be quiet compared to other pumps!

Fortunately it can be pretty easy to adjust the volume by putting the misting pump around a corner or behind a wall. But you can also help that by choosing a pump that runs fairly quietly.

The decibel rating (dB) is a common measurement of sound. 0dB is inaudible -- it's below the level of average human hearing. 120-140dB is where sound becomes painful. Some manufacturers list decibel ratings which will give you an idea of how noisy it will be. These may range from 28dB (about as loud as a quiet living room) up to 68dB (about as loud as an average conversation or a dishwasher) and more.

The actual noise level your chosen pump will make can vary from what the actual rating is. The actual level can be affected by how the pump is mounted, what the area is like around the mounted pump and how close people are to the pump when it's operating. So just a reminder that decibel ratings are to give you a general idea of noise levels.

Helpful Pump Features

As powerful and well-constructed as most misting pumps are, they still need to be maintained regularly. And since they can be so expensive, all sorts of features are available to help you understand them, maintain them and get the most out of them. Here is a list of some of these useful features.

Dry running - most pumps need to have water already running through them before they are turned on. It's usually a simple matter of turning on the water, waiting briefly, and then turning on the pump. Running those types of pumps without water already in them can really damage the pump. But some misting pumps are designed to work without the water running through them. This means these pumps would not be damaged if the water supply is interrupted for any reason.

Duty cycle - lets you know how long you can run the motor at a time. You might assume that you would run any pump for however long you need it. It's true that some pumps work this way. These are called "continuous duty" pumps. Some of these can even run 24 hours at a stretch. But many pumps need frequent breaks.

These are called "intermittent duty" pumps. One example of these is a particular Medium pressure misting pump that can only run for five minutes at a time and then must be turned off for at least one minute. This frequent stopping and starting is done automatically by the pump, itself. Intermittent pumps may reduce the cooling effect somewhat, but they may also be less expensive to purchase and operate.

Filters - are designed to remove sediment, rust, and sand from all the water entering your pump help prevent pump and pipe corrosion as well as nozzle blockage.

Low flow safety switch - Although mist pumps are designed to handle a certain range of water pressures, major fluctuations in the water supply can cause serious damage to a pump. One way to deal with this is to select a pump that runs dry (see above). Another option is to use a low flow safety switch which shuts off the system and prevents pump damage or failure due to low water supply or high system by-pass.

Seal monitors - Seals are designed to handle all the friction of the pump's moving parts and act as a cushion between them. Because they handle so much stress, all seals will wear with time; so their design and material are important for longest seal life. Monitoring the seal wearing helps you know when it's time to replace the seals without risking the pump's failure. Failure would damage the pump and stop use of the misting system until repairs can be made.

Safety valves / regulators - All high pressure misting pumps require some type of safety valve or regulator to balance the misting system's water pressure.

ALL High pressure systems should have both a primary and a secondary safety valve installed for added protection in case the primary valve fails.

Solenoid valves - act like a switch to turn water on or off in case there is an electrical outage.

Thermal relief valve - shuts off electricity to the system when the pump in is danger of overheating. This can happen if water supply is interrupted.

Low voltage controls - Though misting pumps are designed to work within a certain range of electric voltages, large fluctuations can damage it. Low voltage controls will protect your pump in case of "brown outs", "black outs", or other causes of electricity fluctuations.

Pressure switch - tells the pump when to turn on and off. Pressure switches come in different ranges... like 30 to 50 psi or 2 to 4 bar. What that means is if the pressure of the water going into the system is too high or too low, the pump will shut off, preventing damage to the system. But as long as the water pressure going into the system is within that range, it can run safely.

We talk about the second part of misting systems, lines and connectors, here.

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