Seals for mixers

Seals for mixers

What are the different types of seals used in mixing equipment?

Seals are used in mixing equipment to isolate the contents and conditions of the mixing vessel from the surrounding environment. In some processes, mixing would have to be carried out under pressure or vacuum conditions. This would require proper sealing of the mixing vessel. Likewise, mixers which handle hazardous or toxic materials are to be well sealed so as to prevent the leakage of material into the surrounding atmosphere.

The different types of seals used in mixers are as follows:

i)        Lip seals

ii)       Hydraulic seals

iii)     Stuffing boxes

iv)     Mechanical seals

Lip Seals

 Lips seals are also known as elastomer seals as they are manufactured from elastomer. This is the simplest type of sealing arrangement, where the inside face of seal is mounted on the mixer shaft, and held in position by a spring. The outer periphery of the seal is firmly housed within a stationary seal housing. This arrangement prevents exposure of the vessel contents to the outside environment. However, the usage of lip seals is limited to atmospheric operation.

Hydraulic Seals

 Hydraulic seals can be used for atmospheric operations; where in the operating level of the material to be mixed is below the mounting position of the seal. An inverted cup is attached to the rotating mixer shaft; the cup rotates within an annual space provided on the top of the vessel. This annular space is filled with a sealing hydraulic fluid (generally water). The fluid forms a frictionless barrier between the mixer shaft and annular space, thus sealing the vessel contents from the surrounding atmosphere. Because the sealing is achieved by a hydraulic fluid, this type of seal is termed as a hydraulic seal. Hydraulic seals are commonly used in liquid agitators, as they are inexpensive and easy to maintain.

Stuffing Boxes

 Stuffing boxes are the most common and effective sealing arrangements for majority of the industrial mixing equipment. A typical stuffing box assembly consists of a stationary housing located in the area where the mixer shaft exits the mixing vessel. Multiple layers of soft, deformable packing glands are placed within the housing and are compressed using gland followers to prevent the leakage of process material into the surrounding environment.

Stuffing boxes are used in both vertical and horizontal mixers. In horizontal mixers, the stuffing box area is likely to be exposed to the process material and some leakage may take place. The leakage can be controlled by compression of the gland packing through proper tightening of the gland followers. Over tightening should be avoided as it can lead to wear of the packing material and mixer shaft.

Mechanical Seals

 Mechanical seals are used when mixers are to be operated under pressure or vacuum conditions; or when materials are hazardous, toxic and cannot be exposed to the surrounding atmosphere. Mechanical seals are also used in mixers which process high value materials where in no product contamination is permitted.

Mechanical seals consist of two finally lapped flat ring shaped surfaces, one of which is stationary and the other that rotates with the mixer shaft.  A rotating seal is formed between these two seal elements in close proximity to each other.  Depending on the number of seal faces, mechanical seals are classified as single or double mechanical seals. Mechanical seals are expensive and require special attention for maintenance.

Need a Mixer,

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Unique Mixers & Furnaces Pvt Ltd
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Need a Mixer,

Contact us:

Unique Mixers & Furnaces Pvt Ltd
Contact Person: Mr Jayesh R Tekchandaney
Email- sales@uniquemixer.com,jayesh@uniquemixer.com
Phone – +91-22-25801214/25822385
Website – www.uniquemixer.com