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  1. Thealanator

    VFD's and Reciprocating Loads

    Anyone have experience with VFD's on motors that drive reciprocating pumps or compressors? My gut tells me the pulsating currents would not be good for electronic components.
  2. Thealanator

    pump damage?

    We have a centrifugal pump that is started with the discharge valve wide open. Valve is closed after 10 seconds. Of course, the pumping-of-gravel sound is present while valve is open. The pump is started once, and sometimes 2 or 3 times a day. The pump runs far back on its curve (about 15 GPM...
  3. Thealanator

    NPSPR vs NPSHR

    When it comes to reciprocating pumps for cryogenic fluids, the industry apparently likes to use NPSPR as a figure for comparison. The problem I see is that this particular figure is specific to a fluid. Is it safe to use the feet/psi conversion formula to get an "NPSHR" for a reciprocating...
  4. Thealanator

    Question about Pumps

    We are in the review stage of a project to install a fluid cooler that will service four compressors. I think the compressors will require 50 GPM each for cooling. Height will be ~13 feet (3 feet from buried pipe to pump and 10 feet from pump to top pipe on the fluid cooler. We plan to install...
  5. Thealanator

    Cooling Standby Compressors

    We are planning to add compressor capacity. Compressors will operate intermittently. There are lots of ideas related to cooling. One proposal says get two coolers-each cooler sized to handle the total compressor load (1 cooler for 4 compressors). Another proposal says turn off cooling water to a...
  6. Thealanator

    Diaphragm Compressors

    Has anyone had experience with diaphragm compressors? I understand one can get large compression ratios because the diaphragm has a large surface area in relation to the gas flow rate. Is there a limit on the low end of suction pressure (can they go down to atmosphere)? Do they last?
  7. Thealanator

    Bouncing Level Indicator

    We have several liquid nitrogen tanks equipped with Barton level indicators. One of the tanks is pressurized with nitrogen gas through a regulator and solenoid valve. When the solenoid is opened the level indicator starts bouncing 1-2 times per second. Bouncing stops after the solenoid closes...
  8. Thealanator

    Coded Relief Valves?

    Questions about relief valves and compressors: If I consider a multistage high pressure recip compressor I think I understand coded relief valves. The interstage pulsation bottles and heat exchangers are pressure vessels. Coded pressure vessels need coded relief valves. Things get murky when I...
  9. Thealanator

    Desiccant Size for Moisture Removal

    For removing moisture from compressed air (1000-3500 psig in our case), molecular sieve seems to be the compound of choice, especially if you need low dewpoints. Is there an advantage to using type 5A compared to 3A? Would a synthetic oil molecule fit into a 5A pore? On the one hand I could see...
  10. Thealanator

    Jockey Pumps?

    If one uses a jockey pump to keep a deluge water system pressurized, which is better: using a spillback valve for minumum flow or cycling pump off and on (assume that the start/stop setpoints are not spread too widely over the pump curve)? Advantages/disadvantages for each method?
  11. Thealanator

    Fan Efficiency???

    A colleague just told me that a contractor changed out some fans on a couple of cooling towers at our facility. He said that the amp draw dropped from 40 to 18 and asked if we might be able to calculate energy savings. Supposedly the blades are of a new design, with a honeycomb structure. My...
  12. Thealanator

    Cooling Packings on Reciprocating Compressors

    How is this usually done? Does one use the intercooler/aftercooler water pump, or a separate source, say, potable water? We had troubles in the past with a cooling tower because the dust, etc. interfered with flow. We then fed packings with potable water, but returned to the cooling tower line...
  13. Thealanator

    ARC valves for cryogenic service

    In the pump forum I have read about automatic recirculation (ARC) valves that protect a centrifugal pump from low-flow conditions. Is there such a thing for liquid nitrogen service, or would one have to use a flow device/valve combination (flow device on pump discharge controlling a valve on the...
  14. Thealanator

    Which Is Better-Recycle or Variable Speed?

    Consider a centrifugal pump acting as a booster for a reciprocating pump operating at a fixed flow rate. The ideal is that the centrifugal pump operates at its BEP and provides the desired NPSP (a). Now suppose the reciprocating pump/lines are being chilled down before starting the...
  15. Thealanator

    Check Valve as Thermal Relief

    Any thoughts on using a check valve as a thermal relief between two isolation valves?
  16. Thealanator

    Centrifugal and Reciprocating Pumps

    I have been trying to understand the flow vs. head business in the case of a centrifugal pump feeding a reciprocal pump. Since a reciprocating pump is a constant-flow device, the flow rate in the centrifugal pump is fixed. Therefore, the centrifugal discharge head is the sum of the suction head...

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