About 90 percent of all process pumps are powered by an industrial electric motor, so the Pump Guy will offer some fractured history on energy, power and electric motors.

James Watt was born in 1736. He was raised and educated in the coal and iron mining region of Scotland. While in school, Watt studied math and science. He eventually became a practicing mechanical engineer. His mission in life was to see machines replace human and animal power.

To his credit, Watt made major improvements to the industrial steam boiler and held the original patents on the mechanical centrifugal governor, the pressure regulator and the rotary steam engine. He also invented devices used in civil engineering and surveying.

Every student of electricity knows James Watt. The electrical power units watt and kilowatt are named for him.

Mining industry’s influence

industrial electric motor

Figure 1. A mine horse at work. All graphics courtesy of Larry Bachus

Mining was a labor intense industry 200 years ago. It still is today. For menial labor, children were sent into the mines before child labor laws. They went to the bottom of the mines because they had small lungs and did not consume the air/oxygen that a full-grown miner would consume.

A man’s muscles can only perform so much work in a day. A man’s skeleton can only support and carry so much weight. In one of mankind’s first attempts at genetic manipulation, the mining industry bred especially small horses that could go into the mines and do the pulling and hauling that a grown man could not do. The smaller horses also left a smaller pile on the mine floor, which the children had to clean.

Horses also worked at the surface. Because most mines are below the water table and sometimes below sea level, they would often flood if not for the horses that removed the water from the bottom of the mine shaft.

The children would take horsehides and cowhides into the bilge of a mine and sink the hides in the accumulating water. Up top, through a secondary mine shaft, a horse was harnessed to a rope through a pulley under a support frame (see Figure 1).

A rope was lowered through the secondary shaft down into the bilge. The children attached the cowhide to the rope, and the horse pulled the hide into a bag of bilge water. Then the horse would march forward, physically lifting the water bag out of the mine. The bilge water was dumped at the surface, normally into a river where the water would eventually find its way to the ocean.

The process was repeated without end to remove the accumulating water, allowing the miners to dig deeper. With pity toward the children and the draft horses, Watt replaced the human and animal labor in the mines with a steam engine.

Energy, work & power

Just as an artist would begin a painting with pencil sketches to establish perspective, Watt began by defining terms and establishing standards. He defined energy as the capacity to perform work and said that work is a force exerted or multiplied over a distance. He defined power as the “rate at which the work was performed.”

Energy, work and power are frequently and indiscriminately used and confused. Actually, these terms have precise definitions. I will offer some examples of each:

  • Energy: I have enough energy in my bicep muscle to lift a 100-pound weight.
  • Work: If I lift a 40-pound weight 5 feet into the air, I have performed 200 pound-feet (lb-ft) of work (40 lbs x 5 ft). Older engineers may have learned the term ft-lb (as in 200 ft-lbs of work).
  • Power: If I perform 300 lb-ft of work within a second, this is power, or the rate at which work is performed. Power units are lb-ft/second, lb-ft/minute or lb-ft/hour.

Watt wanted his boilers to replace the work of a human or horse. Because the horse was the largest source of power that man could dominate in his day in Scotland, he began his quest by establishing what a horse could do.

The development of horsepower

industrial electric motor

The calculation for horsepower

If Watt had been from India or Cambodia, he might have performed his experiments with an elephant. The history of domesticated Asian elephants for military purposes dates back 8,000 years. Indian mahouts use elephants today for farming and forestry.

Watt harnessed a mine draft horse to a rope with pulleys in a support frame. He experimented with different weights and determined that his test horse could lift 550 pounds at a distance of 1 foot in 1 second. So, Watt declared that 550 lb-ft per second was 1 horsepower.

Because of Watt’s scientific experiments almost 300 years ago, electric motors, cars, lawnmowers, trucks, turbines, boilers, jet engines, rocket engines and today’s battery-powered drones are all rated in horsepower.

Watt’s experiments were performed before the development of the metric system. Today, we can say that one horsepower (550 lb-ft/second) is equal to 0.746 kilowatt (the metric term kilowatt is named for Watt).

Oh yes, Watt went to his grave with an important part of the formula. He never told anyone the size or type of his test horse, so we do not know if it was a Shetland pony, a Morgan or a Clydesdale.

PD pumps

Some 3 million years ago, primitive man provided power to the first pump. An early humanoid made an animal-skin bag, tied the bag to a braided grass rope or vine, and lifted fresh water from a river or natural well. The positive displacement (PD) pump was with the early humans at the dawn of civilization. The first pumps were single-acting, reciprocating, one-stroke, sealless PD pumps.

Centrifugal pumps

Primitive centrifugal pumps appeared about 200 years ago, powered by one of Watt’s rotary steam engines. The vertical pump is among the earliest designs of centrifugal pumps. These pumps were designed to elevate ground water to the surface for drinking and crop irrigation. The first of these pumps was put into service before the arrival of electricity to prairie communities.

The purchase of each new vertical pump was accompanied by a steam boiler and rotary turbine to power it. The pump operator would toss firewood and coal into the boiler’s firebox for heat and fill the drum with buckets of cold water from a nearby creek to make steam. The early water pumps would elevate ground water as long as the operator continually supplied the boiler with never-ending supplies of water and firewood.

To this day, many people mistakenly call these pumps “vertical turbine pumps.” These pumps do not behave like turbines. The early vertical centrifugal pumps were powered by rotary steam turbines.

The modern centrifugal pump became practical after Nicola Tesla developed the alternating current (AC) electric motor about 130 years ago. Just because the AC electric motor was invented and patented in 1888 does not mean we had functioning 20- and 50-horsepower electric motors in 1889. Industrial electric motors began replacing the steam boilers used with centrifugal pumps in the early 1930s.

Normally, pumps and motors are separate devices joined at the shaft with a coupling. In the process industries, pumps are maintained in the pump shop while electric motors are maintained in the electric shop. Combustion engines receive care and maintenance in the engine shop.

Power is important to pumps because most industrial pumps are mated to a source of power. The electric motor is the most popular power source for pumps.

In World War II, industrial electric motors were 60 to 70 percent efficient. Centrifugal pumps were more than 80 percent efficient in the 1940s.

In 2016, industrial electric motors are 92 to 96 percent efficient. Centrifugal process pumps are still about 80 percent efficient. And so it goes.

 

The Pump Guy is Larry Bachus, a pump consultant, author, inventor and closet history buff in Nashville, Tennessee. He is a 30-year member (now retired) of the American Society of Mechanical Engineers. He may be reached at larry@bachusinc.com.