Beacon Engineers Inc

Pump Terminology

Suction Elevation - Elevation difference in feet between the liquid level in the tank or vessel supplying the pump and the centerline of the pump.

Pressure @ Source - Pressure above the free surface of the liquid in the tank or vessel supplying the pump in psig. If the pressure above this liquid is below atmospheric then this number should be negative.

Equipment Pressure Loss - Any pressure losses, in psi, due to filters, heat exchangers, etc. upstream of the pump suction.

Piping Complexity - This term reflects the relative configuration of the piping in which a pressure drop will be estimated for use in this program. If the user does not want the program to automatically estimate the piping losses then "Actual Line Loss" should be selected from this pulldown. If the user does not know the exact configuration of the piping then they can enter the estimated pipe lenght and piping complexity and the program will estmate the line losses for them. The default value, "Normal Piping" should be used in most cases. If your piping application conforms more closely to one of the other options listed, choose that option. This term is used along with the estimated pipe length to determine the friction line losses in the pipe in question at the design capacity. A factor is calculated by your choice and is multiplied by the "Estimated Pipe Length" to arrive at an equivalent pipe length used in determining the piping friction losses in this application. This graph shows the values for this factor and how they change with piping size and pipe routing complexity. If the user calculates and enters their own "Actual Line Loss" then "Actual Line Loss" should be selected in the Piping Complexity pull-down. In this final case, the complexity factor and estimated pipe lenght boxes are ignored by the program

Enter "Actual Line Loss" if Selected - This is a required field if the user selects "Actual Line Loss" for the Piping Complexity. This means that the program will not calculate the line losses for this section of pipe and the line losses in psi entered manually by the user will be used as the pressure loss. Since the program's automatic line loss calculations are based on fully turbulent flow of Newtonian fluids, applications that do not meet these requirements will require that the "Actual Line Loss" for this section of pipe be entered here. Most common cases where this will be needed are for laminar flow applications and situations involving non-Newtonian fluids like pulp stock solutions.

Discharge Elevation - Elevation difference in feet between the liquid level in the tank or vessel at the end of the piping system (where the velocity of the liquid goes to zero, like in a tank) and the centerline of the pump.

Pressure @ Destination - Pressure above the free surface of the liquid in the tank or vessel the end of the piping system in psig. If the pressure above this liquid is below atmospheric then this number should be negative.

Safety Factor - The pressure drop entered here helps account for any inaccuracies in the pressure drop estimations for the equipment, valves, or piping in the system, or changes in the pressure drops in these items over time. These inaccuracies usually arise because of lack of complete information about the overall pumping system or changes that occur over time. If your system has a properly designed control valve in it, the assignment of a safety factor is only of minimal significance because this valve can compensate for changes in the nature of the pressure drops of the individual components in the system. If your system does not have a control valve in it, then the accurate calculation and input of the various pressure drops present in the system becomes extremely important. This is due to the fact that if these individual pressure drops are in error, the pump may not be able to perform to design conditions. In these cases, the assignment of a safety factor is critical. It is better to have a pump that is a little larger (and more expensive) then required than one that cannot pump the fluid to its final destination at all! Of course, the larger the pump, the larger the capital cost, the larger the risk. In this program you have the option to choose from a few pressure drop values for this safety factor, or you can choose to set the safety factor at "10% of the discharge friction loss". This final choice takes 10% of the sum of all the pressure drops (excluding the control valve pressure drop) you entered into the program, and assigns this value to the safety factor pressure drop. In essence this adds a 10% "safety factor" to all the pressure drops you assigned in the program. In most cases this is a good first choice for this safety factor value.

Control Valve Pressure Drop - This value is the pressure drop of the control valve for the discharge side of the pumping system at design conditions. This value should not include pressure drop for manual valves in the discharge piping because these drops should be included in the "line loss" section of this program. In this program you have the option to choose from a few pressure drop values, in psi, for this control valve, or you can choose to set this pressure drop at "33% of variable system loss". This final option assigns 33% of all the losses in the discharge line of the pump (including the safety factor and the control valve drop) to the control valve itself. In many cases this 33% value is a good first choice before the system is fully designed. After the control valve has been designed and specified, this pump calculation should be revisited to make sure the assumptions made here are still valid. Proper control valve design is critical to proper operation of the pumping system in the various conditions it may experience, thus proper engineering design, not just a suggestion from this program, should be conducted to arrive at its final pressure drop value and configuration.

Highest Point in Pipe Rack - Highest point that the liquid must travel in the discharge section of the pumping system. This point may be higher than the Discharge Elevation mentioned above. It is required that you compare this with the total discharge heat of the pump to make sure the pump can get this liquid past this initial height on startup. After the liquid passes this height initially it will recover this head as it falls to its final destination (so long as the pipe is not vented at this high point).

NPSH - Net Positive Suction Head. This is the absolute pressure at the suction inlet of the pump. If this value is not high enough than when the liquid is pulled into the pump the absolute pressure on the liquid in the pump can fall below the vapor pressure of the liquid at the operating temperature. If this happens then the liquid will start to vaporize. This is called "cavitation". As this partially vaporized liquid moves to the discharge side of the pump the pressure increases and the vaporized liquid will "collapse". This can reduce the pumps performance and greatly damage it. Cavitation should be avoided at all times. To do this make sure that the NPSH Available is always larger than the NPSH Required by the pump you choose for your application. This program calculates NPSH Available and NPSH Specified. The NPSH Specified is 2 feet less than the NPSH Available, and the NPSH Specified is what you should use to determine your pump choice to insure that no cavitation will occur in your application. NPSH calculations are usually only significant in pump design and selection when you are dealing with liquids that are heated near there boiling points, or have a suction condition that is under vacuum.

Brake Horsepower (BHP) - The horsepower required to move the liquid in the pump in question. This factor includes the inefficiencies of the pump. The actual electrical horsepower needed will be slightly higher because it must also account for the efficiency of the electric motor driving the pump.

Beacon Engineers, Inc.Phone: 425-869-4141Fax: 425-883-2171Email: smv@beaconengr.com 1999 Beacon Engineers, Inc.