Difference between Long pattern & short Pattern ROSOV
- In petrochemical industry in tankages & terminals all designs are govern by API standards and flanges of valve are design as per API 600 standard ( which is a gate valve standard also )and it is to note that Long pattern of butterfly which is having same face to face of gate valve , its flanges are also design as per API 600 standard and during commissioning of valves for mating tank nozzle flanges which are also design as per API 600 standard there is a compatibility of mating both valve and nozzle flange of tank to assemble them with buts & bolts. Whereas short pattern flanges of Butterfly valves are design as per ISO standard and there is a compatibility issue in mating with the Nozzle flange of tank. Due to which there will be play in both flange mating resultant leakage of hydrocarbon which is very hazardous.
- Also to note ,ROSOV are required for emergency closing of tank with a very less or minimum closing time of less than 5 to 3 second and due to quick closing there will be high surge in amount of pressure is exert on the valve disc ( this pressure which is total of pipe pressure and gravitational pressure which will exert more due to hight of tank as tank height which could be around 9 meter). Due to certain surge in pressure on disc which has to be evenly distribute to the body of valve by the disc , long pattern body & disc will sustain such surge in pressure as due to long pattern body there will be pressure drop from the high surge decrease to normal were as there could be breakage in disc in short pattern as here valve body is smaller and could not sustain such high pressure and disc has to absorb such high pressure and many times causes breakaways which could be very hazadours.
- It is being observed there is a seating issue in short pattern as compare to long pattern valve because after certain time due to wear and tear and impingement effect seat would not be proper amalgamation of seat and seal resultant leakage in valve after some time were as such issue is not observed in long pattern as long pattern body will nullify the impingement effect and valve will give zero leakage for the very long service life.
- Also to note due to emergency closing there is a hammering effect in short pattern valve as due to backward surge in flow pressure which causes due to flowing in back ward direction by fluid due to quick closing as there will will be less space for the fluid to flow and will flow back. Were as long pattern design nullify such hammering effect as their will be pressure drop in fluid flow due to long pattern as fluid has to cover more distance resultant pressure drop.
Looking at such above points it
is highly recommended to use long pattern in comparison to short pattern
specially at the tank nozzle and aloo the tankage using companies -IOCL ,BPCL
,HCPL are using long pattern design only.
