I have two questions:
Could you please help me to select the suitable mechanical seal for VS4 pump for sour crude oil? Some believe that because in VS4 the liquid level in sump is below the discharge flange, mechanical seal is not required. Do you agree?
If both VS1 and VS4 handle our application which one do you select?
Dry gas seal if you need to prevent vapors in suction area from escaping. Otherwise, no seal required.
Continuous duty and/or part of a real process, VS1. Intermittent duty and/or just draining a sump (flow control not important) VS4.
Additionally, VS4 curve shape is generally very flat, it is difficult to determine what flowrate is based on differential pressure, pump will be damaged if it does not operate at appropriate flowrate. VS1 curves will generally be steeper, so it is easy to adjust flow and have a good idea of the flowrate by checking the differential pressure across the pump.
VS4 efficiency is usually very low compared to VS1, so for continuous service the utility costs will be too high.
VS4 are good at emptying sumps using level switches (high level pump turns on, low level pump turns off) and they are cheaper than a VS1. Beyond that, if you have a “real” process that requires a specific head and flow, with some flexibility in adjusting the conditions, then you want a VS1.
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