Ski resorts today use HKD tower guns and/or fan like snow machines. There are 2 hydrants for each and every snow machine or snowgun. One hydrant of course is the water. We must have water because thats the "raw" material for snowmaking. And the 2nd hydrant is the air hydrant. Now you might be asking, "why do you use air to make snow"? Well let's take it from the begining. Water is pumped from a lake or other water source where water travels through a network of pipes, into water hoses to the guns. Now air comes from huge air compressors also known as A/C's where compressed air travels through another network of pipes, then into air hoses, and finally to the guns.
Air & Water Mixing :
Every snowgun is designed in one way or another to mix air & water together. Most snowguns resorts use are "Y" shape guns. Air enters in one branch of the "Y" and the water enters at the other branch of the "Y". Then after the air meets the water, the compressed air shatters ( breaks down ) the water into tiny particles properly sized to become snow crystals, then launched through a nozzle and presto, snow. When compressed air is released to its normal atmospheric pressure, the compressed air expands with the water where the compressed air forms a nucleus around the water particles resulting snow on the surface. Why can't we just sprinkle water to make snow ? You cannot just get a hose and sprinkle water on the grass and expect snow to form. Even if you have special nozzles that creates a fine mist. Water has a high heat of fusion and will expand causing ice, not snow. In order to make snow using no compressed air, you will need about 150 pounds per square inch ( P.S.I ) of water. Ski resorts use around 90 P.S.I of water and around 100 P.S.I of compressed air.
Compressed Air C.F.M :
Another measurement when we deal with compressed air is C.F.M also known as Cubic Feet Per Minute. Some snow guns operate using 180 C.F.M or higher when making snow. Take it this way the higher the C.F.M the more snow we produce per hour. When using a lot of air we must have lots of water. For example, we are using 40 C.F.M of air @ 100 P.S.I and using 70 P.S.I of water. What's going to happen ? The water pressure is lower than the air pressure so the air is going to hold back water therefore water will not mix with the air. Aire pressures and water pressures must be the same. Or 5 - 10 P.S.I off from equal pressure.
Going back to the designs of snowguns. There are more designs than just a "Y" design. Another design is a "T" gun design. In this case water enters from the bottom of the "T" and the air enters from the top left branch of the "T". Air and water collide or mix then launched through a nozzle and presto.
Snowmaking Ingrediants :
There are ingrediants when making snow. They are :
( 1 ) Water
( 2 ) Compressed Air
( 3 ) Low Humidity
( 4 ) Cold Temperatures
( 5 ) Electricity
We talked about ( 1 ) and ( 2 ) earlier. Lets talk about the 3rd ingrediant. When making snow the humidity must be right. If temperatures are marginal the humidity levels must be low. When temperatures are well below freezing, humidity does not matter. Sometimes if temperatures are in the mid 20s and the humidity levels are around 90 % snowmaking will not be possible! The air is so saturated that the compressed air cannot nucleate the tiny water particles. So its not just the heat its the humidity! The 4th ingrediant is temperature. In order to make snow you must have temperatures at 28 degrees ( F ). But what if temperatures are 31 or 32 degrees ( F )? Well you actually can make snow under one condition. The humidity must be very low. We made snow at 33 degrees ( F ) because the humidity levels allowed us to. And the 5th ingrediant is electricity. Air compressors use electricity or fun snow machines use electricity.
Air Compressor Investments :
Ski reosorts spend $500,000 dollars each year for running the compressors. Air compressors are very expensive, each compressor runs about $50,000 per copy. Most resorts have 4 - 7 A/C's. The C.F.M from these compressors are so high that 4 compressors can operate around 300 snow guns at a time. A ski resort called Killington, VT has 7 compressors. Killington has 1,850 snow guns, 600 of those are HKD tower guns and 1,250 are ground guns.
Air Hoses & Water Hoses :
After making snow for a long period of time, snowmakers drain out the water from the water hoses. How? Compressed air ; compressed air blows out the water from the hoses to prevent freeze-ups. Then snowmakers disconnect all the hoses, air and the water hose. Can air hoses freeze up too ? Sure can. Humidity condenses in the hose forming a rime-ice on the inside wall of the air hose causing a freeze-up. Since there hoses are so huge in diameter, very rarely do air hoses freeze.
Key Abbreviations :
A/C - Air Compressor(s).
P.S.I - Pounds Per Square Inch.
C.F.M - Cubic Feet Per Minute.
S.C.F.M - Standard Cubic Feet Per Minute.
Bar - Barometric Air Resistance.
kPa - Kilopascals.
Kg - Kilogram.
In/Hg - Inches Of Mercury.
Mb - Millibars.
mm/Hg - Millimeters Of Mercury.