Halogen: A group in the periodic table consisting of five chemically related elements. Fluorine, bromine, chlorine, astatine and iodine.
Hard face: The face of a mechanical seal (rotating or stationary). Usually made from hard materials, e.g. silicon carbide, tungsten carbide, etc.
Harmonic vibration: Oscillations that are periodically sinusoidal.
Hastelloy "C": An alloy chiefly composed of nickel, molybdenum and chromium. Used in mechanical seals due to its corrosion resistance and insensitivity to halide stress corrosion.
Hazen-Williams equation: Is an equation that relates the flow of water in a pipe to the properties of the pipe, and pressure differential caused by friction. Has been superseded by the Darcy-Weisbach and Colebrook equations.
Head: A term in fluid mechanics to represent the energy stored in a fluid due to the pressure exerted on its container. Measured as a length of fluid where a standard of 10m is equal to one atmosphere, or 14.7 psi.
Helium Light Band: When using interferometric methods to measure seal face flatness, the helium light band is used as a measure. It’s length equals 0.0000116 inches or 0.3 µm. Seals are usually manufactured to a tolerance of 3 helium light bands in flatness.
Horizontal pump: A pump where the rotating shaft is horizontal, as opposed to vertical.
Horse power: A measure of power, the rate at which work is done. One horsepower = 746 Watts. Initially adopted to compare the output of steam engines to the power of draft horses.
Hot oil pump: A pump that pumps hot oil. Hot oil is typically between 350 and 800 degrees Fahrenheit.
Hot work: Any type of work that produces an arc, spark, or open flame. For example, cutting, grinding, welding of metal, or similar activity. This work requires a permit and trained personnel.
Hydraulic balance: A means of reducing heat generation in the stuffing box by reducing the seal face area subjected to the closing force.
Hydraulic drawings: Drawings that pertain to the hydraulic systems of the instrument, rather than the mechanical components. In a centrifugal pump, this would include the impeller, the volute, any liquid passageways, suction valves, etc.
Hydraulic force: Depends on Pascal’s principle that the pressure in a closed system is constant. Used to produce larger force in one area of a system by applying a smaller force to a second area of the system.
Hydraulic gradient: All the energy terms of the system (for example velocity head and piping and fitting friction loss) are converted to head and graphed above an elevation drawing of the installation. It helps to visualize where all the energy terms are located and ensure that nothing is missed.
Hydraulic power recovery turbine (HPRT): A turbine that recovers energy from a flowing liquid. It recovers energy by reducing the higher pressure to a lower pressure.
Hydraulic re-rate: Re-rating of a pump by modifying its hydraulic parts. The conditions that are re-rated could include operating capacity, speed, differential head, liquid type, temperature, pressure and suction among others.
Hydrocarbon: An organic material composed only of hydrogen and carbon.
Hydrodynamic bearings: Ball bearings that use the principle of hydrodynamic lubrication, for example, sleeve bearings and tilting-pad bearings.
Hydrodynamicforce: Force imposed on an object by fluid flowing over or around it.
Hydrodynamic seal: Uses a rotor with grooves to act as a pump and create an air cushion that the opposing sealing face will ride on. Better performance than a hydrostatic seal.
Hydrogen embrittlement: The process by which metals become brittle after exposure to hydrogen.
Hydrogen sulfide (H2S): A highly toxic component of hydrocarbons. Released upon combustion. Pumps that are in use for hydrocarbons containing hydrogen sulfide require special construction.
Hydronium ion: A water with an extra proton, H3O+. Formed by the transfer of an H+ from one water molecule to another in extremely acidic conditions.
Hydrostatic seal: This is a type of mechanical seal that balances the opening and closing forces of the seal to maintain a controlled gap between seal faces.
Hysteresis: The dependence of a system not only on its current conditions but also on its past conditions. For example magnetic fields generated by applying an increasing electric current to a ferroelectric material changes the response of the material to the future decrease of that same current.