Call Us: (973) 256-3000 Plast-O-Matic Valves, Inc.
1384 Pompton Avenue
Cedar Grove, NJ 07009 USA
double cylinder tank level indicator, shown with PVC connections

Series GL Double Cylinder Wall Tank Level Indicators

Advantages of Series GL Level Indicators:

  • Large 360° viewing area.
  • Custom lengths and connections available.
  • Wide choice of select plastic materials to assure maximum chemical compatibility.
  • Little or no maintenance required.
  • No special hardware required for installation (completely assembled and pre-tested).
  • Can be used as a special purpose pipette.

Design Features

True Blue® Series GL level indicators are designed to indicate the presence or level of liquid in a tank. For use with ultrapure liquids or chemicals compatible with Pyrex® glass. O-ring seals are used on Series GL indicators to assure a complete, safe seal. Pipe sizes are 1/2" and 3/4" NPT. BSP sizes also available. Standard lengths are 1', 2', 3', 4'; custom lengths available.

Materials of Construction

Ends on Series "GL" indicators are Geon® brand PVC (TYPE 1, GRADE 1 Polyvinyl Chloride), Natural Polypropylene, or PTFE. Standard O-ring seals are Viton®. The transparent outer cylinder wall is high impact strength acrylic. The wetted inner wall is Pyrex glass (not compatible with hydrofluoric acid or sodium hydroxide). No metal parts are used.

Pressure & Temperature Specifications

Geon® PVC Ends: 50 PSI (3.4 Bar) MAXIMUM @ 140ºF

PTFE Ends: 50 PSI (.4 Bar) MAXIMUM @ 225ºF

Polypropylene Ends: All threaded connections on Series GL are concentrically machined and designed to handle working pressures up to 50 PSI (3,5 Bar) at 185ºF (85ºC) as well as full vacuum. These connections, however, could leak at almost any pressure due to the unstable nature of the virgin polypropylene under pressure. If such a leak should occur, the threaded connection should be properly fillet welded. Generally speaking, these leak problems are almost non-existent with vacuum applications or pressure under 15 PSI.


dimensional drawing of double cylinder tank level indicator
double cylinder level indicator visual glass table of dimensions

Ordering Information

Pipe Size (NPT or BSP)Nominal Length Feet/MetresPart # w/PVC Ends & Viton Seals
1 / .31
2 / .61
3 / .91
4 / 1.22
1 / .31
2 / .61
3 / .91
4 / 1.22

Above part numbers are for Geon PVC ends. If natural polypropylene ends are required, change "PV" to "PP"; for example: GLO5OPP1. For PTFE ends, change "PV" to "TF" NPT threads will be supplied unless BSP threads are specified.

Operation & Use

When properly installed, Plast-O-Matic tank level indicators are automatic in operation and require little or no attention.

Because of Series GL's visual properties and superior design, it is occasionally used as a visual reservoir or "pipette" for unusual filling or dispensing applications. It is especially effective for visually verifying the dispensing of small, imprecise amounts of corrosive chemicals, as long as they are compatible with the Pyrex inner cylinder.

Installation Considerations

The Series "GL" level indicators, usually mounted on the outside of a tank wall, must be installed vertically and are supplied with female threads. In addition, it is advisable to connect these level indicators to a tank with true-union ball valves. This way the level indicators may be removed from the piping for cleaning or inspection while there is still liquid at that level in the tank.

Although the Series "GL" level indicators are only available up to a maximum nominal length of 4 feet, they can be installed on tanks of greater heights. In this case it is recommended that they be installed in a staggered position where the visual length is uninterrupted. This type of installation will eliminate any visual dead spots. Do not connect them together with pipe nipples as it will create visual dead spots and an unstable assembly.

They should only be connected to plastic fittings. Male threads should be wrapped with PTFE tape or other acceptable pipe sealant and only made hand-tight, followed by a one-quarter turn more using a strap wrench. Greater forces tend to stretch or distort the plastic material which could lead to future rupture. Do not use pipe wrenches, locking channel pliers or vise-lock pliers; all of these create stress in the molecular structure of the plastic. Do not connect to a metal pipe. This could cut into the plastic and also cause a future rupture.

Cylinder Wall Information

Clearly, any flow or level indicator is only as good as the quality of its cylinder wall(s) since this is where the viewing takes place. The transparent cylinder walls used in PLAST-O-MATIC flow and level indicators are chosen for characteristics such as high corrosion resistance, high impact strength, and high light transmission.

The inner transparent cylinder walls used in the Series "GL" indicators are Pyrex, a borosilicate glass of very low alkali content that resists attack from most bases and acids with the exception of hydrofluoric acid and sodium hydroxide. This is the same material used in manufacturing glass pipe that is extensively used in the chemical, food, beverage and pharmaceutical industries.

The outer transparent cylinder walls used in all PLAST-O-MATIC indicators are manufactured of a high impact strength acrylic. This material possesses uniform optical quality and has an extremely high light transmission factor, which is of great importance when the color or clarity of your liquid is a prime consideration. Acrylic cylinder walls are ultra-violet resistant.

Modified & Custom Level Indicators

As specialists in thermoplastic level indicator design for over 30 years, Plast-O-Matic's engineering department can modify existing designs...or create an all-new product for any special application. Depending on complexity, minimum quantities and/or design fees may apply. Please contact our Technical Sales Group at (973) 256-3000 for details.

Links to Web Pages with Specifications for each type of Sight Glass

Please click here for web page specific to Series GX Single cylinder wall flow indicators

Please click here for web page specific to Series GY Double cylinder wall flow indicators

Please click here for web page specific to Series GYW Double-Wall, Wafer Style Sight Glasses

Please click here for the general web page for all Plast-O-Matic Sight Glass & Level Indicators Single & Double Cylinder Wall Flow Indicators, Pyrex & Acrylic Level Indicators

Links to PDF files

Please note that the above web pages are slightly more up-to-date than the .pdf files below, and the charts may print more clearly in the web pages. We suggest you try the above .html format, unless you need the convenience of "forwarding" .pdf files, etc. Thank you.

Please Click here for dimensional specifications, pressure & temperature ratings for all Sight Glasses & Level Indicators PDF format

Please click here for PDF file specific to Series GX Single cylinder wall flow indicators

Please click here for PDF file specific to Series GY Double cylinder wall flow indicators

Please click here for PDF file specific to Series GYW Double-Wall, Wafer Style Sight Glasses

Please click here for PDF file specific to Series GL Double Cylinder Wall, Pyrex & Acrylic Level Indicators

Plast-O-Matic Valves, Inc. 1384 Pompton Avenue Cedar Grove,
NJ 07009 USA Phone: (973) 256-3000 Fax: (973) 256-4745
California Warehouse 4054 Brewster Way Riverside, CA 92501
USA phone: (951) 686-2852 Fax: (951) 686-6328
Email: Legacy home page: please click here