Pumping systems Safety factors

This open system pumping water is at sea level (Figure 2-T). Therefore the Ha is 33.9 feet. The level in the tank is 15 feet above the pump centerline, so the Hs is 15 feet. The friction lo,s,ses in the suction piping give us 2 feet. The water is 70° F so the Hvp is 0.839. The Hi is a safety factor of 2 feet. 

System total heads should be estimated as accurately as possible. Safety factors should never be added to these estimated total head values. This is illustrated by Figure 4.8. Suppose that OAi is the correct curve and that the centrifugal pump is required to operate at point A. Let a safety factor be added to the total head values to give a system curve OA2. On the basis of curve OA2, the manufacturer will supply a pump to operate at point A2. However, since the true system curve is OA, the pump will operate at point Ai. Not only is the capacity higher than that specified, but the pump motor may be overloaded. 

As a member of a design group working on the design of a recovery system for SO, you have been asked to estimate the area necessary for a rotary vacuum filter to handle a zinc sulfite filtration. You are also to determine the horsepower of the motor necessary for the vacuum pump. Do not include any safety factors in your results. 

During the PHEA stage, the analyst has to identify likely human errors and possible ways of error detection and recovery. The PHEA prompts the analyst to examine the main performance-influencing factors (PIFs) (see Chapter 3) which can contribute to critical errors. All the task steps at the bottom level of the HTA are analyzed in turn to identify likely error modes, their potential for recovery, their safety or quality consequences, and the main performance-influencing factors (PIFs) which can give rise to these errors. In this case study, credible errors were found for the majority of the task steps and each error had multiple causes. An analysis of two operations from the HTA is presented to illustrate the outputs of the PHEA. Figure 7.12 shows a PHEA of the two following tasks Receive instructions to pump and Reset system. 

Determination of Reliability Characteristic Factors in the Nuclear Power Plant Biblis B, Gesellschaft fur Reaktorsicherheit mbH Nuclear Failure rates with upper and lower bounds and maintenance data for 17,000 components from 37 safety systems Data for pumps, valves, and electrical positioning devices, electric motors and drives from an operating power plant 66. 

Evaluate each task to determine if the task will require a written procedure. Factors that determine if a task requires a written procedure can be the frequency, criticality, and complexity of performing the task. Other factors can include regulatory requirements such as the OSHA 1910.119 Process Safety Management Rule procedure requirements. For example, starting a simple pump may not require a written procedure because it is a very simple task that people are trained to do from memory. However, starting a compUcated pump with many auxiliary systems or a pump that is critical to safety may require a written procedme to ensure the pump is always started correctly. 

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