Mechanical seals are devices used for containing fluid within a Vessel (Pumps, Compressors, Mixers etc.)where a rotating shaft passes through a stationary housing.
There are two main functions of mechanical seal:
- To contain fluid or gas within a Vessel (Pumps, Compressors, Mixers etc.)
- To maintain pressure within a Vessel
There are broadly three ways for classifying Mechanical seal:
- Classification by Arrangement
- Classification by Design
- Classification by Configuration
In this article we will only focus on classification based on arrangement. As per API 682 4th Edition, basedon arrangement mechanical seals can be classified as follows:
- Arrangement 1: Single seal
- Arrangement 2: Dual seal with buffer fluid
- Arrangement 3: Dual seal with barrier fluid
Arrangement 1 are single seals which means they have one pair of seal faces (seal ring & mating ring) forcontaining fluid within a seal chamber. Arrangement -1 is mostly used for application where leaked fluidpassing through the seal faces are non-toxic, non-flammable and inexpensive. Single seal is a cost-effectivesolution and are easy to maintain. Piping plan for Arrangement 1 is simpler and do not require continuousmonitoring.
Leak-proof engineering provides sealing solution for your pump seal chamber. Our proven design LPA 90S, LPA 45S, LPA 47S which is Arrangement 1, API 682 qualified Mechanical seal have significantly sealed pumpsall around the globe.
Before we move ahead with Arrangement 2 it is important to understand difference between buffer andbarrier fluid
In a dual mechanical seal there are two seals, the one which is in contact with the operational fluid iscalled In-board seal whereas the one which is on the atmospheric side is called Out-board seal. The cavitybetween the in-board and out-board seal contains an external fluid. This external fluid can be buffer orbarrier fluid.
When this external fluid pressure is lesser than the operational fluid pressure then it is called as Bufferfluid and if it is greater than it is called as Barrier fluid.
Arrangement 2 seals are dual seals having two sets of seal faces which are arranged in series. When the twoseals are arranged in series it is called as tandem seal. In this type of seals, the external fluid isbuffer fluid. Since the external fluid pressure is lower than the operational fluid pressure leakage fromthe Inboard seal mixes with the external fluid. In this the out-board seal leakage will be a mixture ofexternal and operational fluid. This arrangement is used where fluid is toxic, flammable and productcontamination are not allowed. Piping plan are complex and need timely supervision.
Arrangement 3 seals are dual seals, having external fluid as barrier. In this the in-board and out-boardseals runs on external fluid. This type of seals is used when product contamination is allowed and whenfluid is highly toxic, flammable in nature. Piling plan are more complex and need timely supervision.
Arrangement 1 seal is cost effective and easy to maintain but cannot be used for toxic and flammable fluidswhereas Arrangement 2 & 3 are comparatively costlier and can be used for containing toxic and flammablefluids.