The Air Handler Mini by Biketube Brand is a powerful and reliable mini pump. At 6.3 inches long, less than 4 oz., it fits in cycling jersey pockets and many bicycle seat bags. Air Handler Mini includes a 2-stage function switch. The HV setting moves maximum amounts of air, and should always be used when beginning to pump a flat tire. The HP mode should be used for High Pressure tires (above 40 p.s.i.) when pumping in HV mode becomes difficult. Begin pumping in HV (high volume) mode, pulling air into the barrel on the back stroke. When the switch is in HP (high pressure) mode, the pump will move less air per stroke, requiring less force to reach higher pressures. Simply push the head firmly on to a Presta or Schrader valve and flip the locking lever up for a secure fit. There is no need to disassemble or thread on. Be sure to support the pump head with the opposing hand while pumping, to avoid damaging the valve. Carefully push the locking lever back down and then pull the pump off of the valve. Keep the supplied plug in the pump's valve hole to keep out contaminants. A second rubber grommet is supplied with the pump, in case the first one ever becomes worn.