Starting a Centrifugal Pump

The objective in starting a centrifugal pump is to minimize the damage to the pump s mechanical seal during start-up. The facilities required for this purpose are  

For an externally seal-flushed pump, open the seal flush flow and adjust the seal flush pressure to the manufacturer s recommended pressure above the suction pressure. If this data is not available, use the pump suction pressure plus 10 percent of the pump s normal differential pressure. The seal flush pressure should not be close to the discharge pressure. This will damage the seal. 

For the more common self-flushed pumps, vapors trapped inside the seal system tubing and coolers must be vented out and displaced with liquid. Otherwise, lubrication between the seal faces will be intermittent during start-up. A few seconds of running a dry seal can cause a year s worth of wear on the seal faces. Do not assume that because you have started up a pump without blowing the seal before, that no damage has been done. 

Clean out the pump suction strainer. Check that the suction pressure gauge is operable and that the connection is not plugged. The unit engineer should have placed a red mark on this gauge showing the minimum required suction pressure to prevent cavitation on start-up. 

Vent the top of the pump case to fill the case with liquid. For a self-flushed pump, starting with gas in the pump case will contaminate the seal flush tubing and cooler with vapor. 

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Standard operating procedures An SOP describes a generic set of instmctions for tasks such as starting pumps, lighting burners, or filling vessels. The SOPs can be used as the foundation of specific procedures. For example, the SOP, How to start a centrifugal pump can be used as the basis for the specific procedure, How to start centrifugal pump, P-100. ... 

The Level 1 operator moves on toward certification as a technician. The foundation documents for this work are the plant-specific operating procedures. So, at the basic level, there will be a procedure on how to start a centrifugal pump, say. The trainee wiU also leam specific operating... 

The reason can be explained by referring to Fig. 1, Up to a certain critical flowrate, Qc, the net-positive-suction-head (NPSH) requirements of a centrifugal pump increase, approximately, as the square of the flowrate [2. Above Qc, however, the NPSH requirements start to increase at a much faster rate — shown schematically in Fig. 1. 

Suppose that we repeat the pump-starting experiment shown in Fig. 9.4 for a centrifugal pump. As in Example 9.3, we let the pump turn at 1800 rpm and have an impeller of 10-in diameter. If the pump is full of water, the pump has a pressure rise of 42 psi so there is no problem with the suction lift other than those discussed before in connection with PD pumps. However, when we start the pump, the fluid around the impeller is air. Therefore, from Eq. 9.9 we know that the pressure rise across the pump is... 

Thus, to get a centrifugal pump going, it is not enough to start the motor. One must also replace the air in the system y/ith liquid. This is called priming. Numerous schemes for performing this function are available in addition, special self-priming pumps have been patented and manufactured. 

The outlet valve of a centrifugal pump should be closed before starting and opened as soon as the pump has reached full speed. On the other hand, the outlet valve of reciprocating and other positive displacement pumps must be open before starting. 

Figure 6.6 Representation of a centrifugal pump curve. Point (1) corresponds to the start of filtration and denotes the point where the filter medium resistance is overcome such that equation (6.18) is satisfied. Point (2) represents a point close to the maximum pressure at which variable pressure filtration could occur any further filtration with the pump would generally be performed at constant pressure.

The correct way to start up a centrifugal pump is with the discharge valve barely cracked open. If the operator starts the pump with the discharge valve wide open, or if he suddenly opens the discharge after initiating flow, the pump will cavitate. Why does this happen ... 

Starting NPSH The required liquid head needed to overcome the inertia of static liquid in the suction of a centrifugal pump. 

So in this chapter of failure analysis and corrective methods, we decided to consider some problems, symptoms, and remedies particular to PD pumps. We re using two tables. The first table lists the few symptoms that send a PD pump into the shop. These symptoms are mated to another column of possible causes listed in numerical order. The numerical causes are on the second tabic starting with the. source of the problem in the left column and the probable cause/suggested remedy in the right column. As you go through the list, you ll see again that PD pumps and centrifugal pumps have a lot in common. Enjoy. 

The experiments were performed in a CINC V-02 separator also known as the CS-50 (15). Two Verder VL 500 control peristaltic tube pumps equipped with a double pump head (3,2 x 1,6 x 8R) were used to feed the CCS. In case of the enzymatic reaction, the low mix bottom plate was applied. To operate the reactor at a desired temperature, it was equipped with a jacket which was coimected to a temperature controlled water bath with an accuracy of 0.01°C. The CCS was fed with pure heptane and pure water, both with a flow rate of 6 mL/min. Subsequently, the centrifuge was started (40 Hz, which corresponds to 2400 rpm) and the set-up was allowed to equilibrate for a period of 1 h. At this point, the heptane feed stream was replaced by the organic feed stream (oleic acid (0.6M) and 1-bntanol (0.9M) in heptane). After equilibration for 10 minutes, the reaction in the CCS was started by replacing the water stream with the aqueous feed stream (0.1 M phosphate buffer pH 5.6 containing 1 g/1 of the lipase form Rhizomucor miehei). Samples were taken at regular intervals and analysed by GC. 

This shows that the pump head is determined primarily by the size and speed of the impeller and the pump efficiency, independent of the flow rate of the fluid. This is approximately correct for most centrifugal pumps over a wide range of flow rates. However, there is a limitation to the flow that a given pump can handle, and as the flow rate approaches this limit the developed head will start to drop off. The maximum efficiency for most pumps occurs near the flow rate where the head starts to drop significantly. 

A number of applications are given in this chapter that detail the capture and recovery of intracellular proteins including recombinant proteins. The initial protein recovery steps, regardless of the source, are usually associated with large volumes and crude solutions, requiring removal of particles and reduction of volume before their purification can take place. Centrifugation, filtration, precipitation, solvent extraction, and batch adsorption are common unit operations involved in the preliminary steps of protein recovery. Expanded-bed adsorption, as described here, is an approach for the initial protein recovery that eliminates the need for clarification and volume reduction. In this process, a crude starting solution is pumped directly onto an... 

The latter requires that the starting product solution be centrifuged, clarified, and at times, dialyzed, before it can be adsorbed on a packed column. In contrast, capturing the desired product by the expanded-bed method is simpler because the crude starting solution is pumped directly on the adsorbent. 

High-pressure specification canned-motor centrifugal pumps can provide the solution for the hardest pumping duties. The pump illustrated in Figures 8 and 8.1 has to pump a corrosive suspension in a continuous flow at a starting temperature of 250°C and an inlet pressure of... 

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