Page 117 - Know and Understand Centrifugal Pumps

Know and Understand Centrifugal Pumps

and friction, can change with temperature or agitation. And both
formulas are based on municipal water with piping adequate for that
service only.
In recent years new equipment has been invented, chemical processes,
piping materials, valve designs, and new technologies not considered
when these formulas were developed with cold water in the 19th
century. There is a need to measure the actual losses once an industrial
plant is commissioned and operations begin. The authors of this book
have developed a formula that permits the measurements of these losses
in a live functioning system. Here it is:

The Bachus 8 Custodio Formula
Also called the DUH!! Factor. You’ll need to gather information from
pressure gauges mounted to the existing system. With the previously
mentioned formulas, the Hf and the Hv are estimated in the initial
phase when everything is new. The Bachus & Custodio method
measures the exact Hf and Hv in any existing system. It doesn’t matter
when it was built.

The Bachus & Custodio Formula is the following:

((APDr - APDo) + (APSr - APSO) x
System Hf and Hv =
SP. gr.
where: AP = pressure differential from an upstream to a downstream
gauge in a section of pipe Dr = Discharge Running, the discharge
piping with the pump running. Do = Discharge Off, the discharge
piping with the pump not running. Sr = Suction Running, the
suction piping with the pump while running. So = Suction Off, the
suction piping with the pump not running. 2.31 = conversion factor
between psi and feet of elevation sp.gr. = Specific Gravity
In general, the Hf and Hv are observed while considering the system.
We’ll see this further ahead. The Hf and the Hv are the reasons that
companies contract civil engineers to design their new plants. Years
later, those design parameters have changed due to erosion and other
factors. Let’s look at the following situation, pumping a liquid from one
tank into another.
This system, although simple, with only one pump, is more or less
representative of all systems. This system is composed of 180 fi of pipe;
40 fi of 6 inch suction pipe, and 140 fk of 4 inch discharge pipe.
This system piping uses fittings with bolted flanges, see Figure 8-5. The
6 inch elbows have a constant (K value) of 0.280. The 4 inch elbows
have a K value of 0.310. The 6 inch gate valves have a K value of 0.09.
The 4 inch gate valves have a K value of 0.15. The 4 inch globe valve