Sight Glasses

Introduction

On Spitzer SF and SK silo trailers, the sight glass is an inspection window fitted to the tank wall. It allows the operator to check the tank contents, load level and condition visually, and to confirm the tank has been fully emptied after discharge — without opening any hatches. It is a straightforward but essential piece of equipment: it gives the operator a direct view of the interior while the trailer is in service and the tank is under working pressure.

The heart of the sight glass is the viewing disc — a transparent element that must withstand continuous contact with moving PE/PP granulate or other bulk material, pressure and thermal loads, while remaining clear. Over time the disc becomes opaque, scratched by abrasive cargo or cracked, making visual inspection impossible. In most cases the entire sight glass does not need replacing; the disc is available as a separate spare part. PHS Magnum maintains a stock of sight glasses and their consumable components — borosilicate discs and conical strainer elements — at Chorula near Opole, so repairs can be carried out without waiting for overseas supply.

Construction and Materials

We supply aluminium classic-construction thread-thread (3-inch) sight glasses with borosilicate viewing discs, and thread-flange sight glasses. Borosilicate replacement discs and conical strainer elements are also held as individual spare parts.

The sight glass body is aluminium — lightweight and corrosion-resistant, the standard material for silo trailer accessories. The viewing disc is borosilicate glass, combining optical clarity with resistance to scratching and thermal shock, which matters given the abrasive nature of bulk cargo. Conical strainer elements are stainless steel.

Sizes and Types

The sight glass range covers two connection types and two sizes of replacement discs and strainer elements — one of the few accessory categories where specific numerical dimensions are documented.

Sight glasses are available in two connection variants: the classic 3-inch thread-thread, and the thread-flange. Borosilicate replacement discs come in two sizes — DN80 (3-inch) and DN100 (4-inch). Conical stainless strainer elements are available in the same DN80 and DN100 sizes. This means that if only the disc or strainer is worn, that single component can be replaced rather than the entire sight glass assembly.

Compatibility with Spitzer Silo Trailers (SF/SK)

Sight glasses and spare parts are selected for tank content inspection on silo trailers, including the Spitzer SF and SK series. A sight glass fitted to the tank wall gives the operator a view of the interior during operation; the classic 3-inch thread-thread configuration is the standard design for this type of accessory.

As PHS Magnum services Spitzer silo trailers and related designs, we select sight glasses and spare parts with reference to the actual tank installation. When ordering, the key details are the connection type (3-inch thread-thread or thread-flange) and — for spare parts — the disc or strainer size (DN80 or DN100), as these determine the correct fit.

Common Failure Modes

In day-to-day service practice, the sight glass disc is a wear item subject to constant contact with moving cargo and to pressure loads. Typical signs that replacement is needed include:

• Disc clouding and scratching — abrasive cargo progressively dulls the surface until visual inspection is no longer reliable.
• Cracked disc — compromises tank integrity and prevents further operation under pressure; the disc must be replaced immediately.
• Worn or blocked conical strainer — restricts proper flow and requires strainer replacement.
• Damaged thread or flange on the sight glass body — prevents a secure seal in the tank wall.

In most of these cases, the entire sight glass does not need replacing — swapping the borosilicate disc (DN80 or DN100) or the stainless conical strainer in the appropriate size is sufficient. When refitting, particularly in the thread-flange variant, it is worth checking the joint seal.

Availability and Despatch

Aluminium classic-construction thread-thread (3-inch) sight glasses with borosilicate discs, and thread-flange sight glasses, are held in stock at Chorula near Opole. Spare parts — borosilicate discs in DN80 (3-inch) and DN100 (4-inch), and stainless conical strainers in DN80 and DN100 — are also available from stock. We despatch by courier throughout Poland and to DACH countries (Germany, Austria, Switzerland).

To identify the correct sight glass or spare part, please provide the connection type (3-inch thread-thread or thread-flange) and the size (DN80 or DN100). For details and a personalised quotation, ask for a quote.

Related Categories

• Inter-flange Gaskets — flange gaskets DN80–DN200, compatible with thread-flange sight glass connections.
• Glycerine Pressure Gauges — stainless steel glycerine gauges for working pressure monitoring.
• Fill-hatch Cover Gaskets — upper filling-hatch gaskets for Spitzer, Feldbinder and Kässbohrer silo trailers.
• Spitzer SF and SK Parts — overview of wear and structural parts for the SF and SK series.
• All Spare Parts — full catalogue of silo trailer parts held in stock at PHS Magnum.
• PHS Magnum Silo Trailer Service — refurbishment, accident repair and specialist silo trailer maintenance.
• pasternak.me — expert portal covering silo trailer service, bulk material transloading and bulk material transport.

See also: This category in the full PHS Magnum network catalogue (all makes) →

Author: Aleksy Pasternak — Managing Partner, PHS Magnum. 20 years in the industry; ISO 9001:2015 internal auditor (DEKRA).