8D Single Spring Mechanical Seal

The 8D single spring mechanical seal is the positive-drive version of the Qixing 8. It shares the same O-ring single spring design and the same +200°C, 20 m/s, 1.2 MPa envelope, but adds a positive drive element (the d1 drive pin) so the rotary face cannot slip on the shaft under high torque. Shaft sizes 10 mm to 80 mm. Buy the 8D single spring mechanical seal direct from the Qixing factory in China at OEM and wholesale pricing.

Why the 8D Adds a Positive Drive

In a standard O-ring single spring seal, the rotary face is driven by spring force and O-ring friction against the shaft. That is enough for steady, moderate-torque duty. It is not always enough when the pump starts under load, reverses direction, or pumps hot viscous media - conditions where the drag on the face can exceed the friction holding it, and the face slips. A slipping face stops rotating with the shaft, loses its sealing contact and leaks. The 8D solves this with a positive drive: a drive pin (dimension d1) mechanically locks the rotary face to the shaft drive, so rotation is transmitted by metal, not by friction. The face turns with the shaft regardless of torque, temperature or starting load.

8D vs 8 - When the Drive Matters

The 8 and the 8D are mechanically identical except for the drive. Choose the 8 for normal hot-water, hot-oil and general high-temperature duty where torque is steady. Choose the 8D when the pump has high starting torque, frequent start-stop or reversal, viscous or high-temperature media that loads the face, or a history of seals that spin out and leak. The positive drive adds a small amount to the cost and the d1 dimension to the envelope; in high-torque hot service it pays for itself by eliminating drive-slip failure.

Specifications

Dimensions Chart

All dimensions in millimetres. The d1 column is the positive-drive pin dimension that distinguishes the 8D from the 8. Shaft diameter d is measured at the seal cavity; the 8D covers 10 mm to 80 mm across 28 standard sizes.

Applications

• High-torque hot-water and hot-oil pumps with frequent start-stop
• Thermal-transfer fluid pumps under viscous load (FKM O-ring)
• High-speed two-pole motor pumps where drive slip is a risk
• Heavy-duty sewage and slurry pumps at elevated temperature
• Pumps with a history of rotary faces spinning out and leaking
• OEM pump platforms specifying a positive-drive high-temperature single spring mechanical seal

Manufacturing

Faces lapped to ≤ 0.0009 mm flatness and verified optically. The drive pin and its seat are machined to maintain positive engagement without binding the axial movement the O-ring needs to follow face wear. FKM O-rings qualified for the +200°C range. Each 8D single spring mechanical seal is dimension-checked and spring-load tested before packing; Certificate of Conformity and material certificate ship with the order on request.

Quotation

Send the shaft size, media temperature, shaft speed and starting-torque condition for a same-day quotation. Stock sizes ship 3-7 days; OEM custom orders 15-25 days. Buy the 8D single spring mechanical seal direct from the Qixing factory in China - manufacturer-direct, OEM and wholesale pricing.