Dry pipe system

[dynamo78]

Hi fellow members. I am being trained in the design of sprinkler and read in the NFPA 13 standard, for dry system, that if the air volume being delivered by the compressor is less than 5.5 CFM at 10 PSI, then an "Air maintenance device" is not required .I calculated the volume of the system to be around 40 Cubic foot. I chose a compressor with 1.6 CFM delivery. I am leaning toward skipping the "AM device" but where is that 10 psi coming from? the hydrant pressure is around 150 psi. Do I have to meet both parameters,volume and pressure limits to skip AMD?
Thank you Bros.

 

[FPengineer_03]

I believe the 5.5 cfm at 10 psi is not a specific reference to supervisory air pressure or water supply pressure, but rather a data point for flow rate from a compressor at a specific delivery pressure. All air compressors have air delivery data that provides the expected flow at different delivery pressures, usually represented by a curve on a graph. When you increase the delivery pressure you decrease the flow rate.

That being said, many people don't really understand the purpose of an air maintenance device. It provides two functions: 1) control the supervisory pressure of the sprinkler system via the pressure regulator and 2) control the flow rate to the sprinkler system via the restricted orifice (typically 1/8"). The reason you don't need an AMD with a small, usually riser-mount, air compressor is that they don't produce enough air flow to overcome the pressure loss from an open sprinkler head, which would either slow the response time of the dry valve or completely prevent it from tripping while the compressor runs continuously.

Remember that if you do eliminate the AMD you still need a check valve in the air supply line to the system to prevent water from backing up into your compressor during a trip event.

 

[dynamo78]

Thank You FP. Are you talking of Compressor "Performance Curve?