20V1T

Sentry 20V1T Sentry 20V2T
A newer single-phase Sentry 20V1T
Company	Sentry Siren, Inc.
Produced	1980-Present
Type	Omnidirectional Electromechanical
Sound output	125 dB @ 100 ft (claimed)
Frequency	60 Hz
Horsepower	20 hp
Voltage	208-230/460 V AC 1 or 3 ph
Preceded by	Sterling Model M Sentry 10V2T
Documentation	Product sheet

The 20VXT (20V1T or 20V2T) is a dual rotor mechanical siren that is produced by Sentry Siren, Inc. Essentially a higher horsepower variant of the 15V2T, the 20VXT is the second highest horsepower siren that Sentry currently offers, only beaten by the 40V2T.

History and design

Following the success of the earlier 10V2T, the 20VXT was introduced in 1980 as the dual toned 20V2T, as part of Sentry's 1980 lineup, alongside the 3V8, 5V and 10V. The 20V2T was the loudest, largest, and most powerful offering that Sentry had upon its release. It was also the most expensive. It would remain Sentry's loudest siren until the late 1990s, when the 40V2T was released. Like all of Sentry's mechanical sirens, it uses the rotor and stator from the Sterling Model M.

20V2T

The 20VXT shares the same design as the 16V1T-B and 15V2T, being a large dual rotor siren with 8 long horns attached to each stator port. Unlike the 10V2T, the 20VXT has equal length horns. The 20VXT comes stock with these horns, however the siren can be ordered with skirts instead of horns if the customer wants it. On older units, these horns are flat at the end, but later production 20VXT units use pointed horns to help keep debris out. The 20VXT comes standard in either single or three phase power. Three phase units are powered by dual sided 20 hp AC motor, while single phase units are powered by two single sided 10 hp AC motors. Single phase units use 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. The 20VXT was originally offered in 8/16 port dual tone as standard, being the 20V2T. The 8/8 port single tone 20V1T was available through special order. In 2014, Sentry decided to make the 20V1T the standard option, with the 20V2T still being available through special order. This decision was likely made to make the siren stand out against the 15V2T, which was cheaper and selling better than the 20V2T while being cheaper. In addition, the siren's range was increased due to being single tone. The 20VXT is rated at 125 dB at 100 ft by Sentry.

Due to being a vertical omnidirectional siren, its design is quite simple and similar to Sentry's other sirens. The siren itself is held up by a 6-legged mount which is directly attached to the bottom stator, which has a cone on the bottom to project the sound from the intakes better. The motor (or motors, if it is a single phase model) is in the middle of the siren, between the two rotors. It is protected by a cylindrical motor cover with ventilation holes to protect the motor from the elements. Notably, due to single phase units using two motors, the motor cover is significantly taller than three phase units, which makes them easy to differentiate visually. The upper intake on the siren is protected by a large rainshield, that keeps debris and moisture out of the top rotor. An eyebolt is also included to make installation easier. The 20VXT comes with 16 horns, all of which are equal in length. On 20V2T units, the 8-port rotor is always located on the bottom, while the 16-port rotor is always on top. The 16-port side has two ports per horn. The horns and both intakes are protected by mesh screens to help keep debris out of the rotors.

The 20VXT's sales have waned over the years, largely due to its competition with Sentry's other offerings. The 20VXT is nearly matched in performance by the 15V2T and outperformed by the 16V1T-B, both of which use less power, while the 16V1T-B also runs on DC power. The 15V2T is less expensive, while cities looking for a larger siren typically choose the 40V2T. This has led to Sentry making the siren into a single tone siren, to make it better stand out from Sentry's other sirens. Whether or not this will allow the 20VXT to succeed remains to be seen, but it is a great and loud siren that has made its mark.

Square Horned 20V2T

Early production 20V2T units used square horns, instead of round ones. These were the earliest 20VXT units produced, and were only made for a short time. Approximately 50 of these units were produced between 1980 and 1981, before it was decided that these were too difficult and expensive to produce. In 1981, the horns were changed to the round design used today. Very few of these units remain today, with the last active unit in Russiaville, IN being destroyed by lightning. Another inactive unit is located in Washington, IN.

25V2T-SC

Another variant of the siren was a specially produced siren for the Holcim cement plant in Portland, CO, and was named the 25V2T-SC. This special unit was designed specifically to be completely airtight, with cement dust being unable to enter the siren's bearings and electrical connections and damaging it. Despite being named the 25V2T-SC, the siren is 8/8 port single tone which technically makes it a 25V1T-SC. The siren was powered by a 25 hp dual sided three-phase AC motor, and used skirts instead of horns to prevent dust buildup. This special unit remained in service alongside the unique 40V2T-SC until sometime between 2015 and 2021, when the sirens were removed. The fate of these unique sirens are unknown.