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  1. smckennz

    Effect of second pump in the line on NPSHr

    A larger, second pump, running at a slower speed will have a lower NPSHR and should be selected to satisfy your available suction conditions. If you install this upstream of the existing pump, and perhaps adjust the existing pump impeller diameter or speed to preserve the combined TDH , you...
  2. smckennz

    Lube Oil sight flow indicator position (w.r.t bearing)

    By having the indicator on the drain line, there is a higher probability that a healthy indication means oil has actually passed through the bearing. A healthy feed line indication means oil is heading towards the bearing but may not get there. Also many supply line indicators have an integral...
  3. smckennz

    CIP problem

    Suggest you check your CIP system for compressed air devices which exhaust into the cleaned space or cleaning solution supply lines. You may be getting some oil carry over which will react with caustic to form suds. Cheers Steve
  4. smckennz

    Centrifugal Pump Efficiency Question

    Lets split some hairs: At a suction head equal to the NPSHR, the pump will, by definition, produce only 97% of the TDH that it would if the suction head was sufficiently high to prevent any trace of cavitation. A portion of the missing 3% will seen as a slight drop in absorbed power, but the...
  5. smckennz

    Problems calculating pump flow

    Hi RJ08 The answer is "no" But I can tell you already know that. Perhaps you might want to elucidate. Clearly the information you have been given is insufficient for the task. Cheers Steve
  6. smckennz

    Best way to estimate parasitic capacitance

    This is, or was a big issue in CI engine diesel fuel injection systems - at least in the older ones with injector pumps. Suggest you search accordingly. Depending on your objective, a simplified static analysis should give you and idea fairly quickly whether or not the parasitic capacitance is...
  7. smckennz

    Double Suction Pump Efficiency Claim 93%

    Hi Geoff wasnt expecting to find you here. 93 is on the high side. The number needs to be referred to the proposed test method, as some codes favour the vendor. It is not unusual for the measurement accuracy to be the decider on efficiency. For example, if the test code permits an accuracy of...
  8. smckennz

    diameter of air core in hydrocyclones

    Hi Sripriyarajendran if you precalibrate your transparent cyclone by filling it with water, and taking photos of known dimensions within the cyclone, you will be able to correct for any refractive effects during operation. Cheers Steve
  9. smckennz

    pressure system help

    Hi bartbb Ap2C2Kp is on the money. Sounds like you need a flow controller. Depending on your required accuracy, a simple variable restrictor may help. Google "Maric"; it may help. Cheers Steve
  10. smckennz

    Auto Recirculation Valves

    Hi Alwayslearning it pays to remember that a pump that is not required can be turned off. While this is not always the case with large pumps, it often is with small ones. Cheers Steve
  11. smckennz

    Rag layer recycle pump

    Hi Scipio Perhaps you should review your dismissal of centrifugal pumps as high shear devices, quantify your shear limits, and adjust your parameters accordingly. Perhaps several centrifugal stages will meet your requirements. As you no doubt know, fine sand is a killer for pumps which rely on...
  12. smckennz

    Modified Francis Vane Impeller

    Hi Srv1 when trimming impellers, the similarity laws do not apply. The reason is that they are for a geometrically similar range of impellers. When an impeller is trimmed the ratio of the overall diameter to the inlet diameter (for example) changes, so the affinity laws do not accurately...
  13. smckennz

    Bottom ash conveyor design change

    Hi Crusty1 I have played around with both, and prefer the wet bottom with drag chain (or belt). The things to watch for with a screw are bridging avoidance, bearing protection and gas sealing. With low ash (no bark or mud) you may get away with a screw; I still use them on coal fired economic...
  14. smckennz

    Need reducers!

    Hi Dextermech thin wall SS tube fittings are commonly used in the dairy industry. If you google dairy tube fittings you should find what youre after, or near enough. Cheers Steve
  15. smckennz

    radiator pressure drop calculation

    Hi there have a look at "compact heat exchangers" by Kays and London, Stanford press. Cheers Steve
  16. smckennz

    Breaking seals, bearings on centrifugal pump

    Hi Mrgu if you are suddenly feeding 30 deg C water into a 160 deg C pump, then some thermal shock problems are to be expected unless the pump design allows for this. If the pump problem occurs after trip and when the cool water is fed into the pump, then you might look further at thermal shock...
  17. smckennz

    Droop Instability

    Hi Pumpdesigner have a look at Pumping Manual (9th ed, Elsevier) chapter 5, "head characteristics". It presents Vanastoja's concepts, in graphical summary form. In relation to sacrificing a couple of percentage points to eliminate the droop, this decision may be outside the designers brief and...
  18. smckennz

    two pumps in series with one vfd for one pump

    Hi Naifmbo yes this is done in certain circumstances, normally to avoid the cost of two VFDs but have some measure of flow control without throttling. It can make a lot of sense on a system where around 50% of the head is static lift and 50% is friction. The normal area of debate is which pump...
  19. smckennz

    What is the meaning of lbm/min/KW

    Hi Trevor P that is indeed a stupid question. What would we have to talk about if we all did things like ask people what they mean? However it sounds like a bid evaluation, and evaluators can look bad if they ask bidders stupid questions. I do it all the time. The lb/min/kW sounds like a...
  20. smckennz

    1400 Deg. F - Insulated Pipe Supports

    Hi Nozzle I have done a few of these using metallic supports and controlled the heat loss by controlling the conduction path. The means of control was by drilling the support to balance the conduction area with load/strength requirements. However there is an inevitable heat short. In my cases...

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