Functionality of the adsorber

A silica gel filter dries the air passing through it and absorbs the water down to a minimum residual value. In the process, the air must flow through the adsorber or have contact with the desiccant through openings. The desiccant changes color to a dark blue-green as it is loaded.

Reasons for lack of color change

If an adsorber is mounted on the system for a long period of time without the color of the silica gel changes, this can have several reasons.

1. The plant has “no” pendulum volume.

This means that little or no air is exchanged with the environment. This happens in recirculating oil lubrication systems or systems with co-rotating cylinders. The quantity pumped out of the tank returns to the tank at the same time. Thus, no air is sucked in and, in the case of an adsorber with valves, there is no contact between the silica gel and humidity.

In the figure you can see that an adsorber with valves and no air flow, shows no discoloration and no water absorption.

2. Plant has no air exchange.

This is often the case with gear units if they have only a very small air cushion, are shielded from external weather conditions or are only very rarely in operation.
An example of this are gearboxes for weirs of water navigation authorities. Here, too, valves have a positive influence on the maintenance interval and the water input into the adsorber.

3. Air does not flow through the adsorber

If there is an opening on the equipment through which the air can be sucked in, it will not be dried. Thus, the air bypasses the adsorber. The adsorber does not absorb water and remains in a new state for a longer period of time.

4. Adsober, or the desiccant are oily

Silica gel loaded with oil has lost its ability to adsorb water. The pores are impregnated and thus closed. The color change takes place only partially, with a long delay and with a different hue.

Verification options

Basically, the following applies when using an adsorber: “Only change when the bulk is completely discolored!” However, a delayed color change or no color change can occur due to the points mentioned. To nevertheless ensure that the adsorber protects the system, the following can be done:

Check the flow in the adsorber by “blowing”. The differential pressure of an adsorber is minimal. The air flows through the adsorber by “blowing” through the port. If a higher pressure is required, the adsorber is sticky (possibly due to oil) and must be replaced.

Weigh and compare adsorbers. The weights of all adsorbers can be found in the instructions, data sheets and on the Internet. If there is a difference between the nominal weight and the actual weight, there could be a foreign substance (e.g. oil) in the adsorber.

Send adsorber to GIEBEL FilTec and have it checked. Of course, any adsorber can be sent directly to us.
We check the adsorber, regenerate the silica gel and can thus determine whether foreign substances have been absorbed and what the status of the adsorber was.

NOTE: It is advisable to replace an adsorber (or spare parts package) after two years at the latest.  This ensures safe use of the adsorber and protection of the system!