THE HEART OF A GREAT MISTING SYSTEM
Do Misting Systems Need a Pump?
All misting systems need a misting pump with one exception – low-pressure systems and units that work with gravity-fed water pressures. Running water supplied to most households is usually suitable for low pressure systems. But even those low-pressure systems would require a pump to raise the very low pressure of still water (from a tank, pond, or reservoir) high enough to create some cooling effect. Low-pressure systems can cool things off a bit, but they can also get things wet. Pumps can increase that water pressure to 700 PSI (pounds per square inch) or more. Higher water pressures like these can cool reliably by up to 30º or more without getting anything wet.
There are 3 basic components to a misting system:
- the misting pump, which we talk about here
- the lines & connectors
- the nozzles determine how much water is used.
All these components need to work with whatever pressure the pump provides. Low-pressure systems and units can handle inexpensive plastic components. But mid- and high pressures could easily damage them. High pressure systems won’t be damaged by low pressures, but like a shower head, they need more volume and pressure to get a good spray.
Misting Pumps Manage Water Flow Rate (Volume) and Water Pressure
“Pump” is a simplified term for the pump and the motor combination. A single unit houses the pump and motor. It controls water quantity and water pressure. The misting pump manages the amount of water flow (“flow rate” or volume of water). The motor creates the pressure.
The water in your misting system needs enough volume and pressure behind it to force it through the tiny nozzles that create the mist. You can get a sense of how that works by observing your bathroom shower. When you turn the water on low (low volume & pressure), the water just dribbles through the small holes of the shower head. But when you turn the water on high, 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 like 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 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 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.
Advantages of Tank-fed Misting Systems
The pump completely supplies the water pressure for reservoir or tank-fed systems, such as portable units. 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. You can control the water temperature with these. Since there is a limited amount of water available in tanks, you may be able to chill the water for more cooling effect, especially in more humid weather. You can also control the composition of the water – water can come from any reliable source, and perhaps a drop of peppermint oil in the water would increase the cooling effect.
NO PUMP: Low-pressure, gravity-fed systems – about 20 – 120 PSI / 1-8 BAR.
PUMP USED: • Low-pressure tank-fed
• Mid-pressure systems – 100 – 250 PSI / 7 – 17 BAR and
• High-pressure systems – over 250 PSI / 17 BAR
How Much Water Pressure Does a Misting System Need?
“Flash evaporation” can reduce temperatures by over 30ºF / 16.5ºC . This requires water pressure of at least 700 psi. High-pressure pumps ensure this kind of water pressure and cooling. While low- and mid-pressure can’t match this, they do offer some cooling.
Low-pressure Misting Systems and Units
Low pressure systems and simple units work with the typical water pressures you might find at home from a garden hose. 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. 35 psi / 2.4 bar is considered the minimum water pressure for low-pressure systems.
These systems can have some cooling effect because some of the droplets they produce are small enough to evaporate midair. But the water pressure simply isn’t strong enough to force the water through the extremely small holes that can create flash evaporation reliably. While most water comes out of these as a mist with varied droplet sizes, some tends to dribble out in drops that get things wet and have little cooling effect.
This can be great for people who don’t mind getting wet: kids playing outside, on the sports sidelines, a casual group that might laugh getting a little wet.
Low-pressure systems would need a pump if the water is drawn from a still source, like a pond, reservoir, or tank. Entry-level pumps, called “booster pumps” raise the pressure from still water and typical home supplies to about 160 psi / 11 bar. These can still get things wet but can also achieve more cooling effect.
Medium Pressure Misting Systems
Medium-pressure misting pumps raise the pressure up to 200 – 300 psi / 14 – 21 bar. These are more efficient than low pressure systems and will get things less wet, while still being relatively affordable.
High-pressure Misting Systems
High-pressure systems give the maximum cooling of any misting system – even in areas with high humidity – without getting things wet. High-pressure is generally anything over 250 psi (17 bar). But these systems usually range much higher – in the neighborhood of 800 – 1500 psi (55 – 83 bar). All components of a good high pressure system are rated to work together within the same range of water pressures.
Following are some typical temperature reductions you can expect with a high-pressure system. Low- and mid-pressure systems will have less cooling effect:
- as much as 10° F / 5.5°C in areas with humidity above 80%: Rio de Janeiro, Brazil; Bangkok, Thailand; Darjeeling, India; Darwin, Australia
- as much as 20°F / 11°C in areas with humidity between 40% and 80%: Orlando, FL, USA; Sydney, Australia; Vancouver, Canada; Los Angeles, CA
- as much as 30°F / 16.5°C or more in areas with humidity below 40%: Las Vegas, NV, USA; Cairo, Egypt; Abadan, Iran; Baghdad, Iraq
You can find out the monthly average humidity levels where you live by searching for your city at https://www.timeanddate.com/ (Go to Climate under the Weather tab and Show under the chart.)
It may be possible to move up from a booster to a mid-pressure pump to get more cooling effect with your current low-pressure system; it depends on the components of your current system – the lines, connectors, and nozzles. All system elements need to be able to handle that extra boost in water pressure without being damaged.
The Setup Affects the Water Pressure and Pump Choice
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 systems. But low- and medium-pressure misting systems may suffer from small drops like these. In those cases, even low-pressure systems may need a misting pump to maintain usable water pressure and flow.
In shopping for low- and mid-pressure pumps, look for a bit extra water pressure to allow for these drops.
The Flow Rate (Volume, or Quantity) Affects How Far the Mist Will Reach
A great misting system balances water pressure and flow rate with nozzle size and number. The flow rate helps determine how far the mist will reach from the nozzles.
System Size Influences Choice of Misting Pump
A misting system’s size is determined by the number of nozzles it has. As a standard, they are placed 2 feet apart. Many pumps will indicate how many nozzles they can handle at their designated water pressure.
Basic Misting Pump Specifications
Pump manufacturers typically do not post all of the specs listed below and some may include specs not listed here.
Water Pressure (PSI / bar)
We talk about water pressure levels above and how the water pressure can affect the cooling effect. Look for the PSI / bar number for a misting pump, rather than “low-, mid-, or high-pressure.”
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 115 volts, which is a standard US household current, or in the range of 230 volts. Commercial pumps may operate in the range of 400 to 460 volts. Make sure the pump’s voltages and frequency are compatible with your electricity supply.
Flow Rate / Volume / Quantity (GMP/LPM)
This balances with the water pressure and nozzle sizes to determine how far from the nozzles the mist will reach. Generally, low-flow pumps of .25 to .5 GPM (gallon per minute) or .95 LPM (liters per minute) are suited to low- and mid-pressure systems of about 10-30 nozzles. High-pressure systems can also work with low flows of under 1 GPM / 3.8 LPM for smaller systems in the range of 7-15 nozzles, or up to almost 5 GPM / 19 LPM for 150-200 nozzles, depending on nozzle size.
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 are standardized for economy and availability, while others are customized and specific to your application. Customized pumps can be pre-assembled pump systems, aggregates, modular units, fabricated systems or multiple pump systems, to name just a few. You can also customize them by power source or feature – you might need a system powered by a hydraulic motor, a gas or diesel engine for portability, battery-powered, or solar-powered, etc. The result of this customization is a tailored solution for your needs.
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. 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.
Misting Pumps for Portable Systems
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 there is a limited amount of water available in the tanks, it’s possible to control the water. The water can be chilled – great for more humid areas, and composition can be monitored – water can come from any reliable source or can have additives (a drop of peppermint oil, perhaps).
Misting Pump Noise Levels
The noise from a pump can 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 and neighbors about noise levels 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 simple to adjust the volume by putting the misting pump around a corner or behind a wall or screen as long as it does not interfere with water and electricity access.
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 decibel ratings are just to give you a general idea of noise levels.
|Bottom threshold of human hearing||10dB|
|Quiet living room||30dB|
|Quiet office or library, refrigerator||40dB|
|Average office noise, clothes dryer||60dB|
|Average conversation, dishwasher||70dB|
|Typical home music volume||90dB|
Helpful Misting 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. Some may be optional features you can add to a standard pump.
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. The pump does this all automatically. Intermittent pumps may reduce the cooling effect somewhat, but they may also be less expensive to purchase and operate, saving you on water use and electricity.
Filters – remove sediment, rust, and sand from all the water entering your pump to help prevent pump and pipe corrosion as well as nozzle blockage. These can greatly decrease maintenance and keep your system working longer.
Low flow safety switch – Although mist pumps 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.
Low voltage controls – Misting pumps work within a certain range of electric voltages, so 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.
Seal monitors – Seals 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. 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.
Timer – A timer can reduce water and energy use. Some timers can shut the system down while others can adjust the frequency or intervals of the the spray.
Your misting pump, whether permanent or portable, should have safety features designed to address the risks of using water near electricity. Because it operates near water, your pump may include a solenoid valve, thermal relief valve, or GFCI plug to shut off the pump to prevent damage. Commercial pumps may adhere to the SSC safety classification. See our page on electrical safety outdoors for more information.
We have some surprising tips on what to look for and how to shop for a system in Selecting a Misting System.
Other Outdoor Cooling Methods
Take a look at our comparison page or our pages on other outdoor cooling methods.
While misting systems work well on their own, they can combine with other cooling methods, such as outdoor fans for added cooling effect. Misting fans are a clear example of how misting systems work with another cooling method to maximize cooling. Outdoor shades are a nearly universal solution that work well with any outdoor cooling method.
Swamp coolers (desert coolers) use a similar technology as misting systems, but in a contained unit.
Portable air conditioners are especially suited to enclosed areas and special circumstances.