This glossary serves to introduce the user to the terminology used by Lee Company engineers in describing out products. These descriptions are proposed to serve as a reference point in product discussions to eliminate problems of definition. While these terms are subjected to different interpretation throughout various fields, it is proposed that these definitions be adhered to aid efficient communication.
Accuracy is the degree of error between the intended, specified, or nominal property value and actual value. Typically used to define the performance envelope of a production lot of parts about the specified nominal. Normally used to relate single-event performance of multiple parts. Compare to REPEATABILITY (PRECISION).
Temperature of the media surrounding external surfaces of a valve.
Backlash (Mechanical Hysteresis):
Backlash is defined as the amount (usually in microliters) of "play" or error in the mechanical drive of the pump assembly. This is only noticable when the motor armature changes direction. The error is the result of the clearance between the screw and nut portions of the drive. Properly accounted for with drive software, the backlash can be made insignificant to accuracy and precision.
The maximum pressure a valve can endure before it will break.
See CROSSOVER VOLUME
Coefficient of Variation (CV):
CV is defined as the standard deviation of a distribution of data divided by the mean value. This value, expressed in percent, reflects the degree of spread of data and is used to define the consistency of the performance or of dispensed volumes or other parameter.
Voltage at the electrical connector pins in which the coil must energize if the valve is to perform as stated in the specifications.
Coils rated for continuous duty are designed to be energized continuously without overheating to failure.
Crossover Volume (Dead-leg Volume, Carry-over Volume):
Crossover Volume is any internal-geometry-dependent volumetric error introduced by the value internal volume between the valving point and the common flow point. Most commonly used in discussions of three-way valves, it refers to the unflushed slug of material between the flowing passage and the closed port seal.
Crosstalk (Intra-port Flow):
Crosstalk is any response-time-dependent flow or pressure variation between any two valves or two ports of a three-way valve. For example, this term refers to the flow that takes place between the Normally Closed and Normally open ports of the three-way valve in the time between the beginning of actuation and the end of actuation, when both ports are partially open.
See CROSSOVER VOLUME
Dead Volume: The actual non-flushable volumes of any component or system flow passages, where a dead-end passageway or cavity could retain materials to contaminate subsequent sample or flow media. This value is highly subjective, as many factors come into play to determine the actual dead volume such as miscibility, viscosity, binding energy, etc. The quantity of the former sample still retained inside the component after flushing with some specified volume is defined as dead volume.
No power applied to the coil. A normally closed valve is closed when the coil is de-energized.
Differential Pressure (ΔP): Pressure difference between the inlet and outlet of a valve.
Duty Cycle: The ratio of "on" time to "total cycle" time. If a valve is on for 2 seconds and off for 8 seconds, the total cycle time is 10 seconds and the duty cycle is 20%.
Energized: Power applied to the solenoid valve coil causing the valve to change state. A normally closed valve will open when energized.
Flushability (Axial Mixing):
Flushability the degree of dispersion or band-broadening introduced by a component into a flowing stream. Sometimes referred to as axial mixing, it defines the stretching of a slug of sample as it passes through a component. Usually discussed in relative or qualitative terms, as the specific definition of this characteristic is somewhat complex.
Normally Closed: A normally closed valve is closed when de-energized, preventing flow. When energized, the valve opens allowing flow.
Normally Open: A normally open valve is open when de-energized, allowing flow. When energized, the valve closes preventing flow.
Operating Pressure: The pressure at which the valve is operating.
Proof Pressure: The level of pressure which may be applied to the valve without causing permanent damage.
The repeatability of any function means consistency of performance even if the performance is not accurate. Used in reference to valve response times or dispensed volumes. Usually specified in terms of the percent tolerance about the nominal, specified, or mean value. Used to express the total variability of a single component over multiple events.
This term defines the lag time between the input of a control signal and the resulting response of the system or component being monitored. Typical use of the response time with a passive component could define the time lag between a pressure pulse input to a check valve, and the time to close or open the valve seat in response to that pulse. The more common usage is in reference to a active components, such as solenoid valves. This term then typically defines the time from the beginning of a normal voltage step-input drive signal, and the pneumatic output from the valve port that is opening or closing as a result of that signal. For further discussion of response times, contact your Lee Sales Engineer.