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 In the recommendations issued by ASME and API you will find numerous installation aids and PLAN numbers. Because DEPAC mechanical seals are state-of-the-art and designed to a high technical standard, many PLAN recommendations are either superfluous or irrelevant. Therefore only the most important recommendations are listed here. Customers can of course also use DEPAC seals with other PLAN numbers. For an overall assessment of the installation aids and their positive impact on seal life, please refer to ASME or API recommendations. |
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| ANSI PLAN-No. 7311 API N0. 1,11 Recirculation Flushing  |
RECIRCULATION FLUSHING DEPAC recommends recirculation flushing only when pumping liquids at a temperature near their evaporating point. In this case there is a risk of the medium between the seal faces evaporating on account of the additional frictional heat, causing the mechanical seal to run dry and then fail. Using this PLAN system it is possible to increase the pressure in the seal chamber, thus reducing the risk that highly volatile media will evaporate. The flush should never be introduced perpendicular to the shaft axle but always in a tangential or axial arrangement. A base bushing should always be used as a throttle in the seal chamber. The recirculation line can or should be cooled in addition. |
| ANSI PLAN-No. 7332 API No. 32 Flushing from an External Source  |
FLUSHING FROM AN EXTERNAL SOURCE Flushing from an external source should be used, if at all possible, to keep a problematic pumped medium (e.g. one with abrasive solid material) out of the seal chamber. The substitute flush medium is in this case a clean, cooled lubricating liquid which is compatible with the pumped medium. The flush should never be introduced perpendicular to the shaft axle but always in a tangential or axial arrangement and at a higher pressure than the pump pressure acting on the seal chamber. When a DEPAC mechanical seal is used, the rate of flushing from an external source can be limited to between 3 and 10 liters per hour, depending on the seal size. A base bushing and a flow meter help to achieve and monitor this low flushing rate. |
| ANSI PLAN-No. 7362 API No. 62 Quench (we recommend only steam or gas)  |
QUENCH For crystallizing media, DEPAC usually recommends a quench of low pressure steam. At temperatures below zero, the use of dry air or nitrogen as quench medium will prevent the risk of ice forming on the seal. Steam and the like is fed from the atmosphere side of the seal in order to keep all the dynamic parts of the seal moist and warm. This prevents the formation of new crystals, and any crystals which have already formed are dissolved or removed by the steam from the seal faces. Hard faces should be used in all of these applications. Silicon carbide (SC) is not suitable because the sticking effect of some crystals can cause the SC faces to break against the drive pins when the pump is started. Tests should be carried out to confirm that steam is compatible with the pumped medium and does not produce unwanted chemical reactions. Pressureless quench sealing devices can be used on the atmosphere side if necessary. |
| ANSI PLAN-No. 7352 BARRIER FLUID for Double Mechanical Seals  |
DOUBLE MECHANICAL SEALS with Barrier Fluid A double mechanical seal with barrier fluid must be used for applications in which the pumped medium is not allowed to get into the atmosphere under any circumstances. In this case the pressure applied to the barrier fluid must be higher than the stuffing box pressure. It is usually sufficient for the barrier fluid pressure to be 1 - 2 bar higher than the stuffing box pressure. It is imperative however to use a mechanical seal which will remain functional and closed if this higher barrier pressure should fail for operational reasons. Double pressure balancing is essential therefore for the seals used in applications with double seals. This ensures not only maximum operational reliability but also the longest possible seal life. |
| ANSI PLAN-No. 7354 API No. 52, 54 Barrier Fluid for Double Mechanical Seals with Thermosyphon System  |
DOUBLE MECHANICAL SEALS with Thermosyphon System When double seals are used, a barrier fluid must be introduced between the two seals so that the outer seal is also lubricated and cooled. This can be performed by a thermosyphon system. It is recommended for the pressure applied to the barrier fluid to be higher than the stuffing box pressure at all times. The use of a separate circulating pump (DEPAC TS 50) to assist the thermosyphon effect is also recommended in order to ensure good circulation of the barrier fluid. |
| ANSI Plan-No. C Heating / Cooling with Cooling Chamber  |
HEATING / COOLING Heating or cooling with a cooling chamber is used when the medium in the stuffing box has to be heated or cooled in order to prolong the seal's life by controlling its temperature. When such a heating or cooling chamber is used, the inside walls of the chamber must be checked regularly to make sure that no limescale forms in this chamber. Limescale works like asbestos insulation and reduces or prevents the heating or cooling effect. With this system it is also important to use a throttle bushing in the seal chamber in order to intensify the heating or cooling effect on the seal. |
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