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  • Users: tonyh
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  1. tonyh

    PD Pump Low Speed Operation Motor Stall

    You need to check that the design is actually capable of doing what you want. If you size a VFD and motor combination for its maximum duty - it will not necesarily have the torque capacity at minimum speed - and this sounds as if it may be your problem. You should get the pump vendor to tell...
  2. tonyh

    Mechanical Seals

    If I understand aright, the question is whether the seal will leak when shutdown and the system is locked in, leading to a call on the thermal relief valve? I would ask the seal vendor for his advice, but I would guess that at these pressures there is a fairly good chance that the seal will hold...
  3. tonyh

    continuous shutdown of a pump [b]

    What do you mean by "stall"? If the motor is stopping of its own accord and going out on motor protection (thermal overload), then your problem is unlikely to just be cavitation. You must be taking far more power than you should be, or something is jamming (and that will do damage)...
  4. tonyh

    Centrigugal Blower

    Power is proportional to density, so this device will need to be robust vs an atmospheric air machine. For low pressure ratio (I assume that it is v.low) gas properties are unlikely to be a major issue - and you should discuss this with the vendor in due course. Flow rate is very low, and...
  5. tonyh

    Ring of bolts shearing off!

    I was not quite clear. Was it the bolts that sheared, or the ring? If the ring sheared and the bolts were intact, the other possibility is that the assembly allowed the bolts to put the ring into bending and you ahve mechanically failed the ring due to bolt loading.
  6. tonyh

    Compressor Output vs. Elevation Change

    To put it another way, to a first approximation the machine will deliver the same suction volume of 100cfm, but the mass flow will drop in proportion to the inlet density.
  7. tonyh

    Overpressurize the M-Seal!!

    Lots of different possibilities - you name it - it can be done. Most commonly in my experience is pressure surge in the line from a fast acting valve - but start and stop with valves wide open is a possibility. Blocked in pump with thermal expansion is also a possibility. If you have designed...
  8. tonyh

    Pump running off BEP

    Note the above comment "IF I accept your diagnosis". It is possible that the problem is associated with running off BEP if you are dealing with high specific speeds, but there are lots of other possibilities for high vibrations in centrifugal pumps, and many run very adequately at...
  9. tonyh

    "affinity laws"... for pd pumps ?!?

    Or to put it another way, the affinity laws for a centrifugal pump do not and are not supposed to be dependent on duty. They are merely a way of predicting the charcteristic curve of the pump when you have a known characteristic curve and wish to make a variation in speed of the pump (or...
  10. tonyh

    Pump Question

    There is no inherent problem in running on the flat part of a centrifugal pump curve; the pump will run at the intersection of the pump curve and the system curve whatever. If you are running pumps in parallel then you would have to beware. In this instance it is normal practice to fit a...
  11. tonyh

    Centrifugal Naphtha pump install design question

    Temperature rise will not be negligible. As a first approximation take no flow power from pump curve, assume no heat loss to the outside, and estimate the amount of liquid in the pump volute. A simple mass times specific heat capacity times Delta Temp = energy input equation will give you an...
  12. tonyh

    High Pressure Boiler Feed Pumps

    Of course depending on the system, someone might reasonably be more scared of running his boiler tubes dry for lack of feedwater than getting into pump problem, and therefore be reluctant to trip his pump. A bit of damage to the BFP is more likely to be repairable than a bit of damage to the...
  13. tonyh

    4 pole versus 2 pole

    I think that we are getting too carried away with only one parameter here. Unless 2 pole or 4 pole is the fundamentally important issue (not in my view, then the whole duty is what matters to determine which pump you choose. I believe that for the right duty, I am perfectly capable of buying a...
  14. tonyh

    MTBF for "centrifugal" pumps

    A very good question to which there is no standard answer. It all depends, and it demonstrates why comparing MTBF between different organisations is fraught with trouble. It depends what you wish to achieve. My own view is that it is does not matter much provided that you are consistent. MTBF...
  15. tonyh

    pump packing

    Mechanical seals are good for pumps designed for them. Be careful if you wish to change from packing to sealed pump, though. Some of the old designs effectively use the packing as a sort of auxiliary bearing. An ill thought out change from packing to mech seal can lead to other forms of...
  16. tonyh

    Flow control centrifugal pump with frequency drive or control valve?

    For good use of VFD you need to consider the system curve. Ideal systems are those where you wish to pump against vee squared pressure drop down a line. Then as you change the flow the pressure required changes nicely. Be cautious in using VFDs where almost all the head for the pump is static...
  17. tonyh

    Can You Spec A Pump with Negative NPSHA/NPSHR

    NPSH is effectively margin before boiling. Negative NPSHA means that your liquid is boiling before it gets to the pump. It will then suffer a further decrease in pressure as it accelerates into the impeller eye. In reality if the flow goes two phase in the suction, your suction pressure drop...

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