Hydraulic components

A wide variety of hydraulic components are available for the types of operation and lubrication described in the foregoing. Those typically employed for agitator applications are shown in Fig. 14.

Thermosiphon reservoir
Standardized 6-liter reservoirs are widely used. They offer a large number of connection possibilities and lend themselves to the use of a variety of attachments such as level gauges, limit switches, cooling coils, pressurization, refilling systems, etc.

For optimally designed mechanical seals, reservoirs with volumes of only about 1.5 liters are sufficient. These smaller vessels have fewer connections, but are nonetheless quite versatile. The use of castings jacketed for water cooling makes them less expensive.

Reservoirs are kept 50-70% full, which allows them to act as expansion tanks. If pressurized, they should be equipped with a pressure gauge, a check valve, a safety valve and a manual pump for refilling during operation. Because thermosiphon reservoirs have supply and return piping connections, they are also suitable for forced circulation with a pump.

Pressure boosters
Pressure boosters use a reference pressure signal to regulate a hydraulic system\'s pressure. Coupling the mechanical seal's buffer fluid to the pressure of the medium being sealed affords the advantages already described and works without any pressure control devices or monitors. Level monitoring to milliliter accuracy provides useful information on leakage behavior.

The pressure booster works on the same principle as a hydraulic cylinder. The cylinder's piston moves axially and comes to rest in working positions (i.e. not at the end positions) whenever the opposing forces are in equilibrium. Because the space around the piston rod is filled with the buffer fluid and the opposing side of the piston is connected to the vessel, the forces are in equilibrium when the buffer fluid pressure is higher in the same proportion as the two surface areas; the spring preload introduces an additional pressure component, see Fig. 15.

The buffer fluid space must be filled free of gases to be able to react incompressibly. Gains and losses of buffer fluid (e.g. as a result of thermal expansion or leakage losses) cause volumetric changes only in the buffer chamber (piston movement). By the same token, altering the reference pressure produces a pressure change in the buffer chamber only.

The standard pressure booster versions, namely VD, VGD and VDH, work according to this principle.

Pressure booster VGD is usable for application up to 40 bar and offers the possibilities of a thermosiphon vessel. VD boosters can be used up to 100 bar; but because direct water cooling at the mechanical seal is always used in this pressure range, no additional cooling can be applied. Pressure booster VDH, which has a hermetically encapsulated piston rod, is used mostly with ESM hermetic seals. As a result of encapsulation, the piston rod is likewise pressurized (A1 = A0), and a constant pressure difference created by the spring is maintained at the seal face over the entire pressure range.

The standard pressure boosters can be equipped as needed with various attachments such as refill pumps, pressure relief valves and monitors. These are required especially for installations with central refill units.