What are the different Bitzer unloaders?

Different Bitzer unloaders

Bitzer Unloading (4/6 M - F range) Bitzer use two distinct types of unloading upon these compressors …. Start Unload S U Capacity Regulating C R Start Unload 1 Start unload is used to provide unloaded start capability and is usually required upon Star Delta Start compressors. Although sometimes found on Partwind start compressors, it’s use is not normally required on these machines. 2 The Head and unloader Stem have the letters S U embossed. 3 Maximum required on one machine is 1 S U unloader. Capacity Regulating 1 Capacity Regulating unloading is used to reduce operational cylinders to a minimum of 2, in steps of 2 cylinders i.e. 1 head at time. 2 Thus a 4 cylinder may have 1 CR head, and a 6 may have 1 or 2 CR heads. 3 As for SU the CR Heads and Stem are embossed C R. IMPORTANT NOTE CR heads & stems are not interchangeable with SU heads & stems. Physical Appearance & differences Physically the CR type has a sprung loaded RETAINED piston, with a small offset pin upon the upper surface. If the head is not embossed, then it is probably a CR type. The SU type has a LOOSE piston, entered into the bore from above, plus a LOOSE fitted return spring is required above the piston, entering into the in built recess around the back of the piston. Effect of incorrect fitment If a CR capacity unloader is fitted or wired in place of an SU then the machine shall start fully loaded, and will mean the machine will remain stalled until the starter changes over from star to delta. This could cause high start current problems, and possibly motor overheat due to excess current draw whilst in star phase of the start sequence. If an SU start unloader is fitted or wired in place of a CR then the machine will fully bypass i.e. stop pumping totally, when the capacity unloader operates in it’s normal mode.