Screw pump in the use of the process can not be empty operation, there must be liquid conditions to work, screw pump is leaking.
When repairing its seals, 85% of seal failures are not caused by wear, but are leaked before wear. When the sealing surface is opened, the solid particles in the medium enter the sealing surface under the action of liquid pressure. After the sealing surface is closed, these solid particles are embedded into the surface of the soft ring (usually the right ink ring). This actually becomes a "grinding wheel" that will damage the surface of the hard ring.
Because the moving ring or rubber ring is fastened on the shaft (shaft sleeve), when the shaft moves in series, the moving ring can not fit in time, so that the sealing surface opens, and the delayed closure of the sealing surface makes the solid particles enter the sealing surface. At the same time, there are solid particles between the shaft (sleeve) and the sliding parts, which affect the sliding of the rubber ring or moving ring (relative dynamic sealing point, common failure). In addition, the screw pump medium will also produce crystals in the friction parts between the rubber ring and the shaft (shaft sleeve), and there will also be solid material in the spring, which will open the sealing surface.
Overheating
Due to the heat generated on the sealing surface, the service temperature of the rubber ring should be lower than the design specification. The service temperature of fluorine rubber and polytetrafluoroethylene is 216 ℃, and that of styrene-butadiene rubber is 162 ℃. Although they can withstand higher temperature, the rubber ring is in danger of continuing vulcanization because of the high heat produced by the sealing surface. Eventually lose elasticity and leak.
Crystallization of the medium caused by heat
The heat between the sealing surfaces will also cause the crystallization of the medium, such as carbon deposition, causing the sliding parts to be stuck and the sealing surface to be condensed. And some polymers are coked due to overheating, and some fluids lose lubrication or even flash because of overheating. Overheating can not only change the condition of the medium, but also aggravate its corrosion rate. To cause the deformation of metal parts, the cracking of alloy surface, and some coating cracks, the balanced seal should be selected in the design to reduce the specific pressure and prevent overheating.
Tolerances
Correct assembly tolerances are necessary for the installation of seals. Shafts (bushings) must have appropriate surface roughness and correct dimensions, but the manufacturer rarely provides tolerance data, which are critical for installation. (depending on experience and common sense) the dimensional accuracy and shape and position tolerance of the seal must meet the requirements of the drawing, and the excessive error will lead to the seal failure ahead of time.
