What are internal and external mechanical seals?
Thread Content
A mechanical seal in which the leakage direction of the sealing fluid between the sealing surfaces is opposite to the direction of centrifugal force is called an internal-flow type mechanical seal； A mechanical seal in which the leakage direction of the sealing fluid between the sealing surfaces is the same as the direction of centrifugal force is called an external flow type mechanical seal. Under normal circumstances, internal-flow mechanical seals are commonly found in internally-mounted mechanical seals (as shown in Figures 1, 2, and 3), while externally-mounted mechanical seals mostly belong to the external-flow type (as shown in Figure 4). Since the leakage direction of the external flow type is the same as the direction of centrifugal force, the leakage volume of the external flow type mechanical seal is relatively large. Therefore, most process pumps in the petrochemical industry use internal-flow mechanical seals; external-flow mechanical seals are only used in corrosive media with low pressure and temperature.
Your understanding of internal and external mechanical seals is correct. An internal-flow mechanical seal is one in which the leakage direction of the sealing fluid between the sealing surfaces is opposite to the direction of centrifugal force; it relies primarily on the pressure within the sealing chamber to maintain the sealing performance. This type of seal is often used in high-pressure and high-speed conditions, as it helps to reduce leaks and improve the stability of the seal. In contrast, in the external leakage type mechanical seal, the direction of leakage of the sealing fluid between the sealing surfaces is the same as the direction of centrifugal force. This mainly relies on the low pressure outside the sealed chamber to maintain the sealing performance. Seals of this type may have a relatively high leakage rate, but they might be chosen for external-flow mechanical seals in situations where the temperature and pressure are relatively low and the medium is corrosive. .
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