Effect under Water, Temperature and Altitude
Operating under water
Drilling under high heads of creates different parameters concerning pressure requirements. When a hammer is operating under a head of water sufficient pressure is needed to unload the hole. This is referred to as “peak unloading pressure” and is calculated by the depth of the water in the hole.
One foot of water in the hole is equal to 0.434 psi (0.03 bar). Therefore, if there is 100 feet (30.5 m) of water in the hole there will be 43.4 psi (3 bar) of back pressure.
Once the head of water is broken, the pressure will drop to the drilling operating pressure. If the inﬂux of water into the hole is great, the drill operating pressure will increase and the drill performance will be reduced. In some applications it may be necessary to utilize a high pressure booster compressor to continue drilling.
Foot of head = 0.434 psi
0.305 Meters of Head = 0.03 bar
Effect of altitude and temperature
Altitude and Temperature have a direct effect on the molecular struct of air. An adjustment In CFM (1/SEC) must be made to accommodate such changes and to provide for eﬂicient drilling.
At high altitudes there are less molecules in a given molecule of air than In lower altitudes. Therefore, when compressor displaces a given volume at higher altitude, the air will be less dense. When less dense air is supplied to a down hole hammer a lower operating pressure will be a result.
For example: operating a down hole hammer at 15,000 feet (4572m) of elevation at a temperature of 50°F (10°C) a down hole hammer would require at least 75% more volume than at sea level to operate at the same pressure.
High ambient temperature has much the same effect on air. At high ambient temperatures the air becomes less dense and at low temperatures the air becomes more dense. These changes also require an adjustment of the air supply.
For example: Operating a down hole hammer at sea level with the ambient temperature at 100°F (38°C) versus 0°F (-18°C) would almost require 20% more volume to operate at the same pressure.
The following table may be used a reference to calculate th to maintain a given operating pressure at different altitudes an temperatures.