3V8

Sentry 3V8
Sentry 3V8-H
Company	Sentry Siren, Inc.
Produced	1980-Present
Type	Omnidirectional Electromechanical
Sound output	107-109 dB @ 100 ft
Frequency	60 Hz
Horsepower	5 hp
Voltage	208-230/460 V AC 1 or 3 ph
Preceded by	Sterling Model M Sterling Vertical Siren
Documentation	Product sheet

The 3V8 is a small omnidirectional siren produced by Sentry Siren, Inc. It is the smallest siren in Sentry's lineup, as well as the cheapest. It has been a mainstay in Sentry's catalogue since its introduction, and has seen use in many places for a wide variety of purposes.

The 3V8 is still in production by Sentry to this day, and is a popular option with fire departments and small towns which lack the budget or need for larger sirens. The standard skirted 3V8 is the most popular option due to its low price, though the 3V8-H is also quite common. The 3V8-H-B on the other hand is uncommon due to being new, and its additional cost not being justified by its performance versus Sentry's larger DC offerings such as the 16V1T-B and 14V-B.

3V8

The 3V8 was introduced in 1980 as part of Sentry's 1980 lineup, which also included the 5V, 10V, and 20V2T, following the success of the earlier 10V2T. The 3V8 is the smallest of that lineup, and is intended for short range use, often by industrial sites or fire stations. The 3V8 uses a small 8-port rotor and stator which is borrowed from the Sterling Model M, which is driven by a 5 hp AC motor.

Like all of Sentry's single rotor sirens, the 3V8's design is very basic, with the rotor and stator being attached to a 6 legged mount which has a cone to project the sound from the intake outwards. The motor itself is placed inside a weatherproof housing, and the siren comes standard with a skirt above the rotor and stator to direct sound outwards. This simple design allows the siren to be both cheap and easy to maintain. The rotor, stator and intake are protected by mesh screens to keep debris out. The 3V8 is available in either single or three phase AC, with single phase units using a centrifugal regenerative brake which slows the rotor down rapidly when the rotor reaches a low enough RPM in order to recharge the motor's capacitor. Single phase units can be visually distinguished from three phase units by their taller motor housings. The siren is able to reach 107 dB at 100 ft. While the siren is normally made of steel by default, Sentry also offers corrosion resistant stainless steel or painted fibreglass (which is designated as the 3V8-F) housings as an option.

3V8-H

As early as the year 1999, a variant of the 3V8 was offered with 8 horns attached to the stator ports instead of a skirt. This is branded as the 3V8-H, and while it is slightly more expensive, the horns increase the siren's performance to 109 dB at 100 ft. Each horn has a screen to help keep debris out. Originally, the horns were flat at the end, however in the 2010s this was changed to use slightly pointed horns which resemble the horn on the Sentry Defender. This is likely to prevent snow buildup in the horns. With the exception of the horns, the 3V8-H is identical to the standard 3V8. These horns make the siren very similar in appearance to the 7V8, but shorter in height due to the 3V8's smaller rotor.

3V8-H-B

In 2015, another variant of the 3V8 was introduced, named the 3V8-H-B. The 3V8-H-B is the DC alternative to the 3V8, running on a 4 hp 42 V DC motor rather than a 5 hp AC motor. This allows the siren to run on battery backup if AC power is lost, and is rated to run approximately 30 minutes after power is lost. The 3V8-H-B comes with horns as standard, and is not offered with a skirt. It uses the same motor housing as the three phase 3V8. The 3V8-H-B can be distinguished by sound from the other 3V8 models by its rapid non-linear windup. It is otherwise identical to a standard 3V8-H, with the same performance.

3V8-HC

The 3V8-HC is one of Sentry's many custom sirens built for customers with specific needs. The Centennial Correctional Facility, which is located a few miles east of Sentry's headquarters, needed a siren to warn of prison escapes and other serious situations at the facility. Because the facility was relatively small (at 40 acres) and was made of sound-deadening thick concrete, Sentry's standard sirens did not cut it. As a result, Sentry took the existing 3V8-H and redesigned the horns to match those used on the 40V2T, with each of the siren's 8 horns being significantly pointed at the top. This helped disperse the sound both outwards and downwards to penetrate the thick concrete. The siren was otherwise identical to a standard 3V8-H. It is unknown if this siren is still in service, and only one was ever built. This siren can be seen as the predecessor to modern 3V8-H units, as in the 2010s the standard 3V8-H gained pointed horns similar to the 3V8-HC, albeit at a steeper angle.

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