Mechanical seals are designed to keep a machine's fluid (water or oil) from leaking into the surrounding environment (the atmosphere or a body of water). Mechanical seals are used on many different types of machinery, including automatic washing machines, dishwashers, and refrigerators. The seal is placed inside the housing wall of the machinery where it contacts the moving part of the pump or motor.
They come in two main styles: piston and diaphragm. Both work by using a rubber/plastic ring to stop water from leaking into the housing. When the motor or pump turns, this ring is pushed outward by the moving part, allowing water to leak past it into the housing.
Piston seals use a series of holes or slots cut into the ring that match up with pins on the casing. As the ring moves in and out, it leaves and enters these holes, preventing any leakage through the seal itself.
Diaphragm seals use a flexible plastic sheet attached to a metal backing plate. One edge of the sheet is wrapped around the shaft that projects into the cavity within the housing. This allows the sheet to stretch as the shaft moves in and out, reducing the gap between the sheet and the casing and therefore the amount of water leakage through the seal.
Seals are found in a wide range of hydraulic components, such as hydraulic cylinders, hydraulic motors, and hydraulic valves. The seals are in place to prevent contamination, especially from dirt and debris entering the machine, as well as external hydraulic fluid leaks. Seals also help reduce noise by preventing the metal parts inside the component from rubbing against one another.
There are two types of seals: mechanical and electrical. Mechanical seals are made from rubber or other elastomer materials that squeeze around the circumference of the component part being sealed. Electrical seals use an O-ring or similar device that stands off the face of the component being sealed. They work on the same principle as a spark plug gap--that is, they allow an electrical charge to pass through but block large objects such as metal-to-metal contact.
Mechanical and electrical seals can be used alone or in combination. For example, a cylinder may have both mechanical and electrical sealing provided by separate pieces of equipment.
The type of seal used depends on what type of contaminant is expected to enter the system and how much access there is to replace them regularly. For example, if moisture is expected to enter the system, then a mechanical seal would be required because they are designed to handle water. On the other hand, if dust is the main concern than an electrical seal would be sufficient because they are self-cleaning.
Mechanical seals play an important role in centrifugal pump systems. These devices protect the pump systems' integrity by preventing fluid leaks and keeping pollutants out. Mechanical seal systems are utilized on different seal designs to detect leaks, manage the seal environment, and lubricate secondary seals. There are two main types of mechanical seals: magnetic and plastic.
Magnetic seals use electromagnets to maintain the seal faces in close proximity. This type of seal is available in single- or double-element configurations. Double-element seals provide improved leak detection over single-element seals because there is more surface area for detecting small leaks. Plastic seals are made from Teflon or other synthetic materials and utilize O-rings as secondary seals. They are available in single- or double-element configurations like their magnetic counterparts.
Mechanical seals can be used in stationary applications such as open-pit mining operations or moving with respect to the seal housing like in rolling mills. Seal designs vary depending on the application; however, they all perform basic functions such as sealing between two surfaces that must remain in close contact but cannot touch (such as the rotor and stator of a motor or the casing of a pump).
Types of mechanical seals include: magnetic roller seals, magnetic ball seals, plastic rollers, and plastic balls.
Roller seals consist of a cylindrical shell with magnetic rings mounted on the inner and outer diameter.
For the lubrication of the seal faces, mechanical seals require clean water or another appropriate liquid. A boundary layer of gas or liquid between the faces of a typical mechanical seal lubricates the faces. The seal must be able to drain this fluid so that it does not cause damage to the bearing surfaces.
Mechanical seals are used in applications where sealing reliability and durability are important. These include:
- Hydraulic systems (e.g., lift gates)
- Food processing facilities
- Chemical plants
- Power generating stations
- Airports (including remote locations where power is supplied by generators)
The mechanical seal was invented in the early 1900s and has been improved upon over time. Mechanical seals are available in two main types: radial-end seals and axial-end seals. Radial-end seals have an angularly-spaced pair of seal rings that rotate with respect to each other, while axial-end seals have a single ring that slides along an angled surface as it rotates. Both types of mechanical seals can be hand operated or motorized.
On the impeller spinning shaft, a mechanical seal is placed. This keeps fluids from seeping through the gap between the pump body and the shaft. Mechanical seals are generally made up of two rings: one rotating on the shaft and one stationary on the pump housing. These rings must be kept apart to allow space for movement of the ring (for example, when the shaft rotates). When installed in a pump, the rotating ring usually has grooves or lips that contact the shaft. The shaft may also have protrusions that fit into these sealing surfaces. These shapes are such that as the shaft rotates, it forces the rotating ring away from the static housing ring. This creates a seal against fluid leaking into the pump.
A mechanical seal is used in pumps to prevent fluids being pumped from coming into contact with the area around the shaft. This would happen if the seal was not present. On low-speed motors the seal may actually be the most fragile part of the pump. That's because there's not much pressure behind it to force it radially outwards. So any foreign object that gets caught between the rings could cause them to grind together, damaging both rings and preventing the pump from working.
The mechanical seal is placed on the end of the motor shaft where it connects to the pump. There are several different types of seals, but they all work on the same principle.