8 Single Spring Mechanical Seal

The 8 single spring mechanical seal is Qixing's high-temperature O-ring single spring seal: rated to +200°C and 20 m/s, with an O-ring secondary seal in place of a rubber bellows. Shaft sizes run 10 mm to 80 mm, pressure to 1.2 MPa. It suits clean water, sewage, oil and moderately corrosive fluids that run hot or fast. Buy the 8 single spring mechanical seal direct from the Qixing factory in China at OEM and wholesale pricing.

Specifications

How Hot Can the 8 Run?

Up to +200°C continuous with an FKM O-ring. The O-ring secondary seal is the reason: FKM holds its chemical and thermal stability to +200°C, where the NBR or EPDM bellows in a standard seal would harden and leak above +150°C. For hot water, hot oil, thermal fluid and hot condensate, the 8 single spring mechanical seal stays sealed where a rubber bellows seal fails. With NBR or EPDM O-rings the same seal also covers cold and ambient water service down to -30°C.

O-ring Seal or Rubber Bellows - Which Lasts Longer in Hot Service?

The 8 uses an O-ring that slides along the shaft to follow face wear, rather than a rubber bellows bonded in place. Two practical differences follow. First, temperature: an O-ring can be FKM and run to +200°C; a moulded rubber bellows is limited by its compound and its bond line. Second, thermal cycling: the sliding O-ring keeps the face in contact as the assembly heats and cools, while a bellows seal can lose face load through repeated expansion and contraction. For pumps that get hot or cycle often, the O-ring single spring design is the longer-lived choice.

Do I Need the 8 or the 8D?

Both share the same +200°C, 20 m/s, 1.2 MPa envelope and O-ring design. The difference is drive. The 8 is driven through the spring and O-ring friction, which is fine for normal torque. The 8D adds a positive drive element for pumps with high starting torque, frequent reversals or viscous hot media, where drive slip is a risk. If the pump is a standard hot-water or hot-oil duty, the 8 is correct; for high-torque or heavy-duty hot service, choose the 8D.

Dimensions Chart

All dimensions in millimetres. Shaft diameter d is measured at the seal cavity. The 8 covers 10 mm to 80 mm across 31 standard sizes.

Applications

• Hot water circulation - boiler circuits, heating systems, hot service water
• Hot oil and thermal-transfer fluid pumps (FKM O-ring)
• High-speed booster and two-pole motor pumps up to 20 m/s
• Sewage, drainage and general industrial transfer at elevated temperature
• Light chemical and dosing pumps (weak acids, alkalis, solvents)
• OEM pump platforms specifying a high-temperature O-ring single spring mechanical seal

Manufacturing

Faces lapped to ≤ 0.0009 mm flatness and verified optically. FKM O-rings qualified for the +200°C service range. Each 8 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 and shaft speed for a same-day quotation. Stock sizes ship 3-7 days; OEM custom orders 15-25 days. Buy the 8 single spring mechanical seal direct from the Qixing factory in China - manufacturer-direct, OEM and wholesale pricing.