Regarding the issue of pump inlet pressure and saturated vapor pressure
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I would like to ask the seniors here: I encountered a problem related to the saturated vapor pressure of liquids when making the selection decision, as the parameter table provided by the client pertains to volatile substances at relatively high temperatures. The saturated vapor pressure of the liquid at this operating temperature is given as 0.11 MPa. I saw on Baidu that the inlet pressure of a pump should be higher than the saturated vapor pressure of the liquid in order to avoid cavitation. But the inlet pressure of the pump is negative, while the saturated vapor pressure is positive; therefore, a comparison cannot be made. In my opinion, if the liquid is close to boiling point, its saturated vapor pressure is very high; in such a situation, a negative pressure at the pump’s inlet will exacerbate the boiling process. I’m quite confused about this. The specific parameters are shown in the diagram – please advise on how to select the appropriate pump for this application!
Vapor pressure is an absolute pressure, while inlet pressure is a gauge pressure; there is a difference of one atmosphere. Pumps with a submersible design, such as vertical sac pumps, can be used to increase the net positive suction head available in the system.
The value on the data sheet indicates positive pressure, and the tangential flow pump 50-25-160 can meet the requirements. In fact, the medium lost 11 meters of head due to evaporation at that temperature; therefore, when selecting a pump, an additional 11 meters should be taken into account to compensate for this loss
It’s that same design institute that uses the S-6 and 304 materials – it really kills people:( Is the red text something you changed, or is it already in the data sheet? The inlet pressure is positive; only the amount of head needed to compensate for the losses needs to be considered, and the design team has specified this clearly. The outlet pressure is 44 meters, but the actual total head is 55 meters
The red parts were provided by the client; they are the aspects I find useful as references. Can it be determined from this table that the solution storage tank is a positive-pressure tank? Otherwise, methanol would have long evaporated at that temperature. Does the saturated vapor pressure provided by the customer not need to be used as a reference value for selection? Because this value is a physical property of a constant.
As long as the inlet pressure is not negative, that’s fine; this can be determined, so you can proceed with confidence. Just increase the head a bit to compensate for the loss caused by the vaporization pressure
How can the inlet pressure be negative?
What does it mean by \"It’s that same design institute that uses S-6 and 304 material – they really ruin people’s lives\"? Could you tell me about it?
S-6 is chromium-molybdenum stainless steel; 304 is more expensive, resulting in a higher overall price
Oh, you mean this. 304 is A-7, right? It seems that when making the selection, people simply use the existing data sheets, filling in the data only without considering anything else. This must be a template; those who filled out the s-6 probably don’t know what it means.
But I do have a question: you said that 304 refers to castings, right, that is, CF8?