Aircast Hand Pump for the FP/SP Walker and S/C CryocuffAircast Hand Pump for the FP/SP Walker™ and S/C Cryocuff are often asked how the pump works. If you just pump hoping the air cells will fill then you are going to have to pump for ages. However, if you hold your finger over the black valve on the inflate end of the pump, as in the picture on the left, then pumping becomes more efficient.