PUMP-NOLOGY

By Gerard J De Santis

In this definitive technical textbook, readers will gain the knowledge to safely engineer and design pumping equipment, particularly in the ultra-high pressure industry, and will be educated in all the technical aspects of mechanical pumps and pumping hydraulics.

• Language: English
• Publisher: Palmetto Publishing
• Release date: Feb 3, 2021
• ISBN: 9781649904911

Gerard J De Santis

Gerard De Santis has more than fifty-three years experience working in the pump manufacturing industry. Gerard was the founder and CEO of Jetech Inc., a company he started in 1988. In addition he has held positions such as application engineer, design engineer, vice president of engineering, and president of a major pump company. He has performed as lead instructor regarding pumping hydraulics and pump design at a host of conferences, both in the U.S. and abroad. He has served as a consultant engineer to utility and manufacturing organizations, and in the legal field served as an expert witness regarding safety aspects of pumping and ultra-high pressure water jetting equipment. He recently retired from Jetech Inc, and holds the title of Chairman Emertus. He continues to work as an engineering consultant.

Book preview

Preface

T

he understanding of hydraulics and the proper application of pumping equipment are two of the most important aspects in the design and analysis of systems involving the pumping of liquids.

Every day in the industrial environment people are involved in the investigation and evaluation of pumps and pumping systems. To properly perform those functions a basic understanding of hydraulic engineering principles as well as knowledge of the operating characteristics of pumping equipment are essential. While there are many articles and texts published intended to meet that purpose few offer the reader a full understanding of why a certain formula is used or discuss the practical side of the theory behind it.

Since there are many different types of pumping machinery in the marketplace, it is the author’s intent to present in this text a straightforward approach to pumping hydraulics and machinery characteristics as they relate to crankshaft-driven plunger and direct-acting pump designs. It is also the author’s hope that the information presented in this text will be used as a reference guide by both the experienced engineer and novices alike.

1

Hydraulics

T

he subject of hydraulics involves the study of liquids in both the static and dynamic states and encompasses topics such as liquid properties, pressure, liquid types and flow characteristics. Before we explore those topics in detail it is important that we define and have a basic understanding of what a liquid is.

Liquid: Unlike other fluids, a liquid is a substance that forms a free surface between itself and its vapor, as illustrated in Figure 1-1.

Most liquids are considered incompressible at low pressure and because of their molecular characteristics they tend to possess a definite volume without any specific shape, as depicted in Figure 1-2.

FIGURE 1-1

FIGURE 1-2

Liquids exist in both the static and dynamic states and depending on the condition they exhibit certain properties that are of importance. For example, when a liquid is in the static condition the properties of density and vapor pressure are of interest whereas in the dynamical condition liquid type, viscosity, and flow pattern are of major consideration.

Liquids are grouped into two major categories: Newtonian and Non-Newtonian. Under the Non-Newtonian class there are subcategories such as Thixotropic, Plastic, and Dilatant. The category into which a liquid is classified depends on how it behaves when in motion. For the purposes of our discussions we will not delve into the theory between those two groups but instead concern ourselves with Newtonian liquids such a water and hydrocarbons.

For additional information regarding the subject of Newtonian and non-Newtonian fluids, please investigate the writings of Sir Isaac Newton (1642–1727), noted Englishman, mathematician, scientist, and inventor.

LIQUID PROPERTIES:

Liquid properties are those characteristics of a liquid such as specific weight, specific gravity, density, vapor pressure, and viscosity. In the following paragraphs, we will define each of those characteristics, how they relate to each other and how they are affected by other factors such as temperature, shear stress, etc.

Specific Weight (W)

Specific weight (normally symbolized by W) is the weight per unit volume of a liquid, and in the English system, it is usually expressed in pounds per cubic foot (lbs./ft3). The W for water at 60 F is 62.4 lbs./ft^3 and is determined by calculating the force a volume of water one cubic foot in dimension exerts on its base of one square foot, as illustrated in Figure 1-3. A simple and approach to determine the W for any liquid is to fill a liquid tight box of inner dimensions 1 foot wide by 1 foot long by 1 foot high with a liquid at 60 F and weigh it.

FIGURE 1-3

MASS DENSITY: ρ

Mass density (symbolized by the Greek letter rho: ρ) is the ratio of the specific weight (W) of a liquid to the acceleration caused by gravity. Mathematically expressed, mass density is shown in Equation 1:

In the English system, the density of water at 60 F is 1.94 slugs/ft3 and is determined by using Equation 1 as follows:

ρ = W/g = 62.4(lbs./ft^3)32.2(ft/sec^2) = 1.94 (lbs./ft^3 × sec^2/ft)

A unit of slug is equal to (lbs. × sec^2/ft.) and substituting this into the above calculation,we get:

ρ = 1.94 (lbs./ft^3) × (sec^2/ft) = 1.94 (slug/ft^3)

Specific Gravity (SG)

Specific gravity (symbolized by SG) is a unitless number and is a useful tool in solving pumping hydraulic problems. The SG value for any liquid can be determined by comparing either the specific weight (W) or the density (ρ) of the liquid to the corresponding units of water at 60 F. Mathematically, the SG value for any liquid at any temperature can be calculated by dividing the W or ρ (depending on the units working in) of water at 60 F, as expressed in Equation 2.

Equation 2

SG = (W at desired temp. F)/(W of water at 60 F) or;

SG = (ρ at desired temp. F)/(ρ of water at 60 F)

Examples of the use of Equation 2 are:

Problem 1

Water at 140 F is to be pumped using a centrifugal pump. As such, it is desired to know the SG of the hot water so that the proper horsepower determination can be calculated. What is the SG of the water at 140 F?

Solution 1

SG (water at 140 F) = (W at 140 F)/(W at 60 F)

SG (water at 140 F) = (61.46 lbs./ft^3)/62.4 lbs./ft^3) = 0.985

Or

SG (water at 140 F) = (1.911 slugs/ft^3)

From this important relationship of being able to determine the SG of any liquid by solving equation 2 using the units of density, we can write an equation that will permit us to determine the density of any liquid at any temperature if the SG is known. The equation takes the form expressed in Equation 3:

Equation 3

ρ = SG × 1.94 slug/ft^3

Refer to a suitable published data source showing the properties of water at various temperatures. Additional examples using Equation 2 follows.

Problem 2

A hydrocarbon is to be pumped at 45 F. Test have been conducted and determined that the W of the hydrocarbon at 45 F is 48.7 lbs./ft3. Calculate the SG at the pumping temperature.

Solution 2

SG = (W at 45 F)/(W of water at 60 F)

SG = (48.7 lbs./ft3)/(62.4 lbs./ft3) = 0.780

Problem 3

A mixture of chemicals is to be pumped at 50 F.