Independent vent carrying flammable vapor from the separator to outside air, separate from sanitary ventingIn: Oil/water separator field guide
Vapor-compression cycle
The four-part loop, compressor, condenser, metering device, evaporator, that moves heat using a refrigerant that changes stateIn: Refrigeration cycle field guide
One variable-speed pump set through the chillers and coils, with a minimum-flow bypass protecting the evaporatorIn: Chiller plant sequencing optimization
Variable retainage / step-down
A contract term that reduces the retainage rate, or caps it, at a milestone such as 50 percent complete; some states require it.In: Retainage and retention field guide
Variable torque vs constant torque
Load type that sets drive duty: pumps and fans (normal duty) vs full torque at low speed (heavy duty)In: VFD install and commissioning
Volts lost in the conductor, and that loss as a percentage of source voltageIn: Voltage drop field guide
VECP
Value engineering change proposal, a contractor-initiated proposal on public or federal work where accepted savings are shared with the ownerIn: Value engineering field guide
A disorganized heart rhythm that pumps no blood; the shockable rhythm an AED is built to correctIn: Electrical shock first aid
Verification
Confirming an alarm is real, by call or video, before police respond; a verified alarm gets priority, an unverified one may get noneIn: Intrusion alarm field guide
Names for the same device that varies motor speed by varying output frequency and voltageIn: VFD install and commissioning
VFD / variable-speed
A variable frequency drive that throttles pump speed to hold a discharge pressure setpoint across changing demandIn: Booster and PRV system guide
VFL
Visual fault locator, a red laser pen that confirms continuity and which physical fiber position lights upIn: MPO/MTP polarity methods
VGB Act
The Virginia Graeme Baker Pool and Spa Safety Act, the federal anti-entrapment law requiring compliant covers and secondary protectionIn: Pool and spa mechanical systems
VGB anti-entrapment drains
Main drains built to the Virginia Graeme Baker Act: compliant covers to ANSI/ASME A112.19.8, dual drains spaced so one body cannot block both, and an SVRS or other secondary system where required.In: Commercial pool construction
Vibration analysis / FFT
Reading mechanical vibration; the fast Fourier transform breaks it into a frequency spectrum that names the faultIn: Predictive maintenance guide
Cameras, a recorder or VMS, storage, and the network that carries the video; designed to capture a scene at a chosen detail levelIn: CCTV system design field guide
Visual line of sight (VLOS)
The Part 107 rule that the pilot or a visual observer must keep eyes on the aircraft throughout the flight, absent a waiver.In: Drone inspection field guide
VLF
Very-low-frequency AC withstand testing, around 0.1 Hz, the modern field acceptance test for shielded MV cableIn: MV cable termination and testing
VLF / partial discharge testing
VLF applies a 0.1 Hz AC withstand voltage; PD testing finds and locates local insulation defects; tan delta reads overall conditionIn: MV termination and splicing
VLT
Visible Light Transmittance, the percent of visible light the filmed glass passes; high is clear, low is darkIn: Commercial window film
A spoken emergency instruction to evacuate or shelter, delivered by the fire alarm or emergency communication systemIn: Intercom and paging design field guide
Void content
The percent of the volume that is connected air space, commonly about 15 to 25 percent, that carries the waterIn: Pervious concrete field guide
Void content / void ratio
The share of a material or stone layer that is open space; the storage capacity of the reservoirIn: Porous and permeable pavement
Voltage class (gloves)
Rubber insulating glove rating, class 00 to 4, by maximum use voltage, for shock not arcIn: Arc flash PPE and clothing
Voltage drop
Volts lost in the cable over distance under load, which dims fixtures at the far end of a runIn: Low-voltage landscape lighting