(1) Hydraulic Components
Shielded pump hydraulic components can be used with the same type of seal pump. They are designed to seal the hydraulic pump motor and the shielded motor, forming a combination that includes a general centrifugal pump impeller, volute housing, and flange connections for inlet and outlet. This design is widely used in shielded pumps today. Don’t miss out on the latest valid orders—get them sent to you free of charge! Also, receive the most recent buyer information in the morning at no cost. Grab this opportunity now!
(2) Bearings
Due to the longer rotor, shielded pumps require two sliding bearings, one at the front and one at the back. Diaphragm pumps demand precise alignment of these bearings; otherwise, they are prone to cracking. Shielded pump sliding bearings are typically lubricated by the liquid being pumped. To enhance lubrication, the inner walls and end surfaces of the bearings that come into contact with the thrust plate are often equipped with groove channels. These grooves can be straight, spiral, or a combination of both. Common materials for sliding bearings include:
- **Graphite**: Soft and self-lubricating, graphite is often impregnated with resin or metal to improve wear resistance. Some graphite bearings are coated with tungsten, chromium, diamond, or plasma-sprayed silicon nitride, forming hard friction pairs that can last up to one year.
- **Silicon Carbide**: Known for high strength, wear resistance, and hardness, it’s an excellent bearing material. With proper use, pure sintered grade A silicon carbide bearings can last up to three years.
- **PTFE-Filled Materials**: For handling highly corrosive media, PTFE filled with carbon fiber or glass fiber is commonly used as a non-metallic option.
- **Ceramic or Metal**: In special applications, ceramic or metal bearings may be chosen.
Since shielded pumps don’t use oil lubrication, they are limited in their ability to handle radial and axial loads. Therefore, the design must incorporate multiple strategies to reduce bearing load. One common method is using a double-volute casing, where two 180-degree staggered volutes divide the fluid flow symmetrically, reducing radial force. However, this structure is complex to cast and rarely used. Another approach is using a circular pump body, which reduces radial force at the shut-off point and at the highest efficiency point, though it slightly affects hydraulic performance. Multi-channel pumps theoretically eliminate radial force, but manufacturing imperfections make complete elimination difficult.
To reduce axial force, automatic thrust balance devices, back-impellers, or balance plates are commonly used. Each method has its pros and cons, and the choice depends on practical experience and overall pump design.
(3) Shielding
Shielded pumps typically have two shielding sleeves: one for the stator and one for the rotor. These sleeves prevent the working medium from reaching the stator windings and rotor core. However, the presence of the shielding sleeve increases the air gap between the stator and rotor, leading to higher eddy current losses and reduced motor efficiency. On average, shielded motors are about 5% less efficient than conventional centrifugal pump motors.
For shielded pumps, especially electric diaphragm pumps, the shielding sleeves must be made of corrosion-resistant, high-strength, non-magnetic materials to minimize energy loss. The design should aim for a compact shielded motor with a thin shielding sleeve. The material should be non-magnetic, such as austenitic stainless steel, Hastelloy, Hastelloy C, or titanium. Among these, Hastelloy produces lower eddy current losses and is preferred for the stator shield, while the rotor shield can be made of either Hastelloy or austenitic stainless steel.
The thickness of the shielding sleeve usually ranges from 0.4 to 0.7 mm. While a thicker sleeve offers better structural integrity, it also increases energy loss. Therefore, the design must strike a balance between strength and efficiency.
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