How to make process inspection easier with sight glass

In closed pipe systems, it is often challenging to know exactly what is going on inside the darkness. Is the product flowing as it should? Is cleaning sufficient? Without visual access, you can easily find yourself groping in the dark. Sight glasses give you the necessary ‘window’ into the process so you can optimise operations, ensure quality and minimise waste time. 

In food, beverage and pharmaceutical production, the requirements for hygiene, documentation and process control are high. That is why much of today's production takes place in closed systems such as stainless steel pipes due to the hygiene and durability of the material. This protects the product from the outside world, but at the same time creates a barrier for the operator and the technical manager. They cannot see the flow in the system. 

Without inspection points, air pockets, product residues or foreign objects can be difficult to detect before they have already caused problems further down the line. This can result in costly production stoppages or, in the worst case, discarded batches. 

Sight glass, also known as inspection glasses, are mainly used in piping systems in, for example, dairies and breweries. With sight glass, you can see in real time whether the flow is stable, whether the product has the right colour, and whether there are signs of foam or coating. This makes it easier to respond quickly and effectively – both during normal operation and when troubleshooting. 

Sight glass adds value in situations where you need immediate visual feedback. 

• During start-up and changeover: Here, the sight glass helps you determine when the product is stable in the piping system, minimising the transition phase. 
• During CIP cycles: The operator can see whether the cleaning fluid is flowing evenly and, most importantly, when the rinse water is transparent. 

The visual feedback makes it easier to make decisions: Should the line be stopped, rinsed longer, or can production continue as planned? 

The location determines how much your inspection points contribute to the overview. Typically, it makes sense to install them: 

• Before and after pumps: To detect air, cavitation or unstable flow. 
• At tanks, exchangers and filters: Where clogging or changed product behaviour can be seen directly. 
• On long lines: Multiple sight glasses along the piping make troubleshooting significantly faster. 

If the product does not behave as expected at the outlet, you can narrow down where the problem occurs step by step. In many plants, it works well to combine fixed sight glasses in the stainless pipes with transparent hoses where flexibility is desired. 

There are several types of sight glass that match different requirements for pressure, temperature and safety. Our range includes sight glasses with and without borosilicate glass, which are used in different situations and process plants. 

When choosing the right sight glass, temperature, pressure and coupling type are the decisive parameters. Borosilicate glass is ideal for high temperatures and pressures – for example in demanding CIP/SIP processes – whereas FEP is the obvious choice if break resistance and chemical resistance are the most important factors. Regardless of the type, sight glass are available with both threaded, clamp and weld connections, so you can easily adapt the solution directly to your existing piping. 

Our sight glass with FEP tube is for food and pharmaceuticals, as the material is tasteless, odourless and chemically inert. It is ideal if you want a glass-free installation to avoid the risk of glass splinters. Available with protection net for high pressure conditions. 

This sight glas offers high strength and stability for environments where a glass-free installation is not a requirement. It is often cheaper than the FEP solution and can be secured with protection net or polycarbonate to withstand pressures of up to 10 bar. 

Our Clamp sight glass is an alternative solution that also uses borosilicate glass, but in a more flexible design. A food-grade cross with welded on clamp liners on the branches can, for example, be a simple and economical way to create a sight glass. The assembly gives the operator a clear view of the flow and makes it possible to quickly inspect selected sections without having to rebuild the pipe system. 

Regular maintenance is key to maintaining operational reliability and extending service life. Sight glass is often exposed to high temperatures, pressure variations and aggressive chemicals. This requires ongoing monitoring and proper care. 

• Gasket inspection: Replace seal rings regularly to prevent leaks. 
• Prevent thermal shock: Avoid sudden temperature changes as they can damage the glass. 
• Cleaning: Use only approved agents. Avoid abrasive cleaners that can scratch the surface. 
• Inspection: Check regularly for cracks, cloudiness and worn gaskets to prevent unexpected downtime. 
• Safety: Use protective screens in areas with high pressure and always ensure correct installation. 

The choice of sight glass should be based on the properties of the medium, pressure and your specific cleaning procedures. 

For more than 40 years, we have been advising customers in the food and pharmaceutical industries, and we therefore have in-depth insight into the requirements and needs of these industries. Contact us today on tel. +45 7020 0422 or email inquiry@alfotech.eu. We are transparent in helping you choose the sight glass solution that best suits your production.