Plan 53m Vs 53B and 53C Plan 53m Vs 53B and 53C hamidabbasi (Mechanical) (OP) 11 Nov 13 06:58 Hi, what is API plan 53M and what is the difference between API Plan 53M and 53B and 53C. when we should use 53M. Best Regards Hamid RE: Plan 53m Vs 53B and 53C flexibox (Mechanical) 12 Nov 13 14:57 Plan 53M is same as Plan 53B. Please refer to API standards for definition of each Plan. A good example where you can use plan 53C is where you have varying high pressures. (Offshore) In this case Plan 53C follows the changing pressures and maintains a delta P. The delta P may is dependant on the piston ratio for example it may be 10% increase on it pulse pressure normally discharge. If you apply Plan 53B to this then the barrier pressure needs to be set to the max pressure and the operating pressure will be high even at lower chamber pressures. Some people have a preference in using Plan 53C. My preference 53B, I like its simplicity. What is your application? RE: Plan 53m Vs 53B and 53C hamidabbasi (Mechanical) (OP) 16 Nov 13 02:34 Dear Flexibox thanks for your kind reply, but my question is about 53M not 53B or 53C. what is the differences between 53M and 53B. RE: Plan 53m Vs 53B and 53C flexibox (Mechanical) 18 Nov 13 05:41 My opening line is plan 53M is same as 53B. RE: Plan 53m Vs 53B and 53C Airsporter1st (Mechanical) 5 Mar 14 10:44 Flexibox is right. 53M stands for 53 Modified and was used to designate a system using an accumulator to store/pressurise barrier fluid. The designation 53M was replaced with 53B quite some time ago, so you probably have an old system/drawing.