Glossary

Ullage - The volume of fluid which a vessel lacks from being full.

Ultrasonic - A vibration with a frequency higher than that normally audible to the human ear.

Unloading Valve - A Valve which by-passes flow to the reservoir when a set pressure is maintained on its pilot port.

Unload - To release flow to the reservoir.

Vacuum Press - A hydraulic press with vacuum enclosed platen working areas to remove air, gas vapors, and fumes during the forming process. A vacuum style hydraulic press ensures consistent material flows, as well as precise control over temperature and pressure.

Vacuum Pressure - A deficiency of fluid or flow resulting from too low temperature, incorrect fluid viscosity or too high suction velocity. Leads to suction difficulties and pump damage.

Valve, Proportioning - This valve is a fixed differential pressure reducing valve and has a fixed spring and a fixed differential area. It is used in brake systems to limit the magnitude of the pressure to the rear brakes.

Vena Contracta - The region of smallest cross section in a fluid stream. As fluid emerges from an orifice, it tends to contract in cross section reaching a minimum and then expanding back to fill the conduit.

Viscosity Index - A measure of the viscosity-temperature characteristics of a fluid compared to two arbitrary reference fluids.

Window Frame Hydraulic Press - A hydraulic press with a large open feed area, or window, designed especially for larger dies, or where access to work area is important. A window style hydraulic press offers minimal deflection and optimal cross head parallelism.

Work Height - The distance from the floor to the top of the bolster.

Water Hammer - The vibration of a conduit in a fluid system due to rapid changes in liquid velocity due to valve closure.

Wear Ring - An element used to prevent cylinder seals from being crushed and metal-to-metal contact from occurring by maintaining seal concentricity when side loads exist.

Wobble Plate - A rotating canted plate in an axial type piston pump which pushes the pistons into their bores as it "wobbles."

X, Port - This refers to a pilot signal port.

X-ray Emission, Proton Induced PIXE - An X-ray emission spectrometer based on physics and not on chemistry. It separates the electrons from the hydrogen atom, then an accelerator drives the protons at a high speed to collide with the target or specimen. This spectrometer is capable of evaluating 72 elements simultaneously in one sample.

Y, Port - Refers to a pilot signal port.

Yield Strength - The stress at which a material exhibits a specified deviation from proportionality of stress and strain.

Young's Modulus - The ratio of a simple tension stress applied to a material to the resulting strain parallel to the tension.

Z Factor - This factor is defined by the relation Z = PV/NRT and is based on the assumption that at the same reduced pressure and temperature all gases have the same compressibility factor.

Zero-lapped - A critical-center condition where the spool land width is identical to the port width.

ZETA Rating - A contaminant abrasivity rating system that allows the Omega Life of a component to be transformed to a Zeta Life to reflect the abrasivity severity of the environmental contaminant.

Z-Transform - Converts the difference equations into algebra form and normally used to handle discrete or digital samples.