Circulating Flushing and Leakage Flushing for Mechanical Seals:
A Simple Explanation

What kind of flushing methods are suitable for the mechanical seals in hygienic twin screw pumps?

Possible flushing methods:

Recirculating and loss flushing are key methods for ensuring the proper functioning of mechanical seals. A common feature of both methods is that the seal fluid is not pressurized. While recirculating flushing circulates the seal fluid, loss flushing specifically drains it away. The two approaches differ in terms of design, effect, and application.

Essentially, using a flushed seal design offers the following advantages:

Cooling

Friction between the sealing surfaces generates heat. The flushing medium dissipates this heat.

Lubrication

The main criterion is that a load-bearing lubricating film is formed between the rotating and stationary sliding surfaces, thereby preventing direct contact between the sliding surfaces.

Cleaning

Another effect is that solids, deposits, or crystals are flushed away, or their formation is prevented altogether. This prevents damage and avoids the seal from becoming blocked and damaged by crystals or solids. This applies in particular to loss flushing, whereas with recirculation flushing, it must be expected that undesirable substances may accumulate in the closed circuit.

Circulation flushing

What is the recirculation flushing process?

With recirculation flushing, the flushing medium circulates in the flushing circuit. In order to achieve the lowest possible pressure loss, the flushing chambers are connected in parallel. This is important for natural circulation.

Advantages

- Rinsing media other than water can be used
- Reduction in water consumption
- Suitable for mobile units

Disadvantages

- Germs can accumulate in rinsing circuits
- Difficult thermal management
- Loss of rinsing medium due to evaporation

Schematic representation of circulation flushing for screw pumps

Agenda:
A = Output
E = Input

Schematic diagram of the connections for a recirculation flush

Loss flushing

What is meant by the process of loss flushing?

The flushing medium does not circulate but is lost after the flow and is not fed back into the circuit. Both flushing chambers are connected in series to ensure that both chambers are flushed during a flow.

Advantages

Very good hygienic properties. Leaks are specifically removed, flushing with condensate possible
Very good temperature control of the shaft seal possible