Alfa Pressure Switch Model PRV 15

Alfa Pressure Switch PRV-15 (7-15 Bar), Auto Cut-Off Switch for Air & Water
Item: Pressure Switch – Suited for Air Compressors
Application: For automatically starting & stopping motors of air compressor and Pressurized water plants
Operation: Smooth and Trouble free with exceptionally long life
Cut-out Pressure Range: 7-15 (Kg/Cm²) / 100-213 (PSI)
Minimum Differential: 1.7-2.3 (Kg/Cm²) / 24-33 (PSI)
Maximum Differential: 7 (Kg/Cm²) / 100 (PSI)
Maximum Amp : 6
Maximum Volts : 500
Phase : Works on Both Single Phase and Three Phase power supply but maximum ampere load on pressure switch should not be more than 6 AMPS. While using 3 Phase motors of higher than 2 HP, it is required to be used with a 3 Phase Motor Starter so that the ampere load goes on to the starter.

Note the V is model number stands for Valve. This is a relief valve which is an additional valve on the bottom of the pressure switch which is designed for certain type of air compressors which provide exhaust relief pipe. That thin copper pipe needs to be connected to this relief valve and it releases the compressed air in the discharge pipe making discharge pipe empty for smooth automatic start of compressor.