this depends on the seal design and what you want to achieve in the seal chamber. Do you have details of the seal arrangement? also some information on the application. For example if you have a Plan 32 injection the throttle bush will help control the flow or likewise if you wanted to increase the chamber pressure with Plan 11 you can do this, so it depends on the arrangements.
According to API 610 10th Ed. Para 5.7.1 Radial running clearances shall be used to limit internal leakage and, where necessary, balance axial thrust. Impeller pumping vanes or close axial clearances shall not be used to balance axial thrust. Renewable wear rings shall be provided into the pump casing. Impellers shall have either integral wear surfaces or renewable wear rings.
Based on this paragraph my understanding is that any pump purchased according to this specification shall have:
1. two casing/impeller wear rings
2. it should have throttle bushing...
API 610 does not require a throat bushing. The only purpose for a throat bushing is to control the fluid in the seal chamber either to increase pressure (for example a plan 11) or to limit interchange with the pumped fluid (for example a plan 23).
Para 5.7.1 only dictates certain design features for the wear rings. It does not dictate the number of wear rings or bushings. In certain circumstances such as high suction pressures with OH2 pumps, only one wear ring (on the impeller eye side) might be fitted to help balance axial thrust.
API 682 notes the optional nature of throat bushings in 6.1.2.15
BTW, the current edition of API 610 is 11th edition.
Thanks a lot guys. One more question, is an open type impeller design acceptable as per API 610? Based on para 5.7.1 my interpretation is that open type is not acceptable.
Please understand something - API 610 IS NOT A SET OF MANDATORY REQUIREMENTS - any provision can be negociated /changed/deleted as per Client's specific requirements
With regard to the open impeller - technically API 610 does not refer to pumps equipped with open impellers - however, I did once purchased one such pump which was designed as per API 610 requierments with the stated exception of the impeller
Thanks pumpkind. However, as we specify on the purchase order that the pump shall be bought according to API 610 Specification, any mandatory requirements "the use of shall" must be followed by the winning vendor otherwise vendor shall state on their "Exception & Deviation" during the bidding stage.
In addition to, if the pump will not be furnished by replaceable wear rings, it will be more costly to change the impeller. Thanks and hoping for additional comments.
API 610 11th edition, explicitly allows open impeller designs, per 6.6.1
Previous versions of API 610 did not exclude the use of open impellers.
I don't agree that 5.7.1 10th edition precludes open impellers. All that paragraph limits is the use of close axial clearances. No reputable manufacturer is going to use close axial clearances on open impellers. For example we use a minimum axial clearance of 0.030" (0.75mm) per side on our OH2, OH3 open impellers, which is well in excess of what is necessary from a thermal transient standpoint.
Hi bradshsi, thanks. However in terms of maintenance cost, pump with replaceble wear rings is benificial than open type impeller...My opinion..how about you...
I tend to agree that maintenance cost on closed impellers will be lower.
Open impeller pumps don't tend to play as well if there are any significant solids in the pumped fluid. When wear occurs, you are replacing larger more expensive components.
Please consider that the need for open impellers comes from the API 610 requirement to select a pump between 80 to 110% of BEP. For very low specific speeds, the only practical manufacturing option is an open impeller. As a manufacturer we will always offer a closed impeller where possible.
