Question 1

What is an elastomer bellow mechanical seal?

Accepted Answer

An elastomer bellow mechanical seal (also called a rubber bellows seal) uses a molded elastomer bellows — NBR, EPDM, Viton, Aflas or FFKM — in place of the springs and dynamic O-ring found in a conventional pusher seal. The bellows flexes to compensate for face wear, shaft misalignment and thermal growth, so the seal keeps face contact even in fibrous, dirty or slurry-laden fluids that would clog a spring.

Question 2

Where are elastomer bellow seals used?

Accepted Answer

Typical applications include HVAC chiller and hot-water circulator pumps, municipal wastewater and sewage lift stations, clean-water booster and potable-water pumps, submersible drainage pumps, pool / spa / irrigation pumps, and low-pressure chemical and dosing pumps.

Question 3

Which OEM seals do Astra elastomer bellow seals replace?

Accepted Answer

AS elastomer bellow seals are direct dimensional and performance replacements for John Crane Type 21, Type 6A and Type 502; Sepco 500 series; EagleBurgmann MG1 and MG12; Flowserve BX / BXR; Chesterton 155; AESSEAL P04; and equivalent rubber-bellow designs on Grundfos, Wilo, KSB, Xylem/Goulds and Pentair pumps.

Question 4

What are the pressure, temperature and speed limits?

Accepted Answer

Standard elastomer bellow seals operate up to 10 bar / 145 psi, −20 to 120 °C (up to 150 °C with EPDM/Viton) and 15 m/s peripheral speed. Balanced designs such as the AS 502 push pressure up to 40 bar / 580 psi.

Question 5

Which elastomer material should I choose?

Accepted Answer

NBR is the low-cost default for clean water, oil and mild wastewater. EPDM is required for hot water, glycol / HVAC service and dilute alkalis (never with oil). Viton (FKM) handles hydrocarbons, mineral oils and mild acids to 200 °C. Aflas and FFKM (Kalrez) are used for aggressive chemical, ozone and steam service.

Question 6

Which face material combination should I specify?

Accepted Answer

Silicon Carbide (SiC) vs Carbon is the general-purpose default for clean and mildly abrasive water. SiC vs SiC is preferred for wastewater, slurries and marginal lubrication. Tungsten Carbide (TC) vs TC handles the most abrasive municipal and industrial sewage duties.

Question 7

How do I identify the right elastomer bellow seal for my pump?

Accepted Answer

Send us either the OEM seal part number, a photo of the failed seal, or the pump make / model plus shaft diameter and service fluid. Our engineering team cross-references it to the matching AS elastomer bellow model — typically AS 2100, AS 502, AS 110, AS 128, AS FBD, or AS SDM — within one business day.

Question 8

Are elastomer bellow seals suitable for hot water and HVAC circulator pumps?

Accepted Answer

Yes — EPDM elastomer bellow seals are the standard choice for HVAC chilled-water, hot-water and glycol circulator pumps up to 150 °C. Never use NBR or Viton with glycol/steam; use EPDM. For cooling-tower and condenser water duty specify SiC vs Carbon faces to handle waterborne solids.

Question 9

Can rubber bellow seals handle abrasive or fibrous wastewater?

Accepted Answer

Yes. Because the bellows flexes instead of a spring, elastomer bellow seals resist clogging in fibrous municipal sewage, pulp-carrying wastewater and light slurry. For heavier abrasive loads specify SiC vs SiC or TC vs TC face pairs on the AS FBD or AS 128, or move to our dedicated slurry & FGD seals.

Question 10

What is the difference between an elastomer bellow seal and a metal bellow seal?

Accepted Answer

Elastomer bellow seals use a molded rubber bellows (NBR/EPDM/Viton/Aflas/FFKM) and are limited to about 150 °C and 40 bar. Metal bellow seals use a welded stainless / Hastelloy bellows with no secondary elastomer, so they handle hot hydrocarbons, steam and thermal cycling up to 400 °C. Choose elastomer bellows for water/HVAC service and metal bellows for high-temperature refinery duty.

Question 11

Are Astra elastomer bellow seals interchangeable with John Crane Type 21?

Accepted Answer

Yes. The AS 2100 and AS 110 are direct dimensional and performance replacements for John Crane Type 21 and Type 6A on standard ISO 3069 / DIN 24960 shafts from 12 mm to 100 mm — same envelope, same face load, same rotation direction. No pump modification is required.

Question 12

What lead time and MOQ apply to elastomer bellow seals?

Accepted Answer

Standard AS 2100, AS 110, AS 128, AS 502, AS FBD and AS SDM sizes ship from stock in 3–7 business days with no minimum order quantity. Custom face or elastomer configurations typically ship in 2–3 weeks. Request a formal quote and lead time confirmation via the Request Quote button on any product page.

Question 13

Are Astra seals compatible with major OEM pump brands?

Accepted Answer

Yes. Every Astra seal is engineered as a direct dimensional and performance replacement for major OEMs including John Crane, Flowserve, EagleBurgmann, AESSEAL, Chesterton, and Sepco. Provide the OEM part number or a photo and we cross-reference it to the matching Astra model.

Question 14

What materials are available?

Accepted Answer

Standard face combinations include Silicon Carbide (SiC) vs Carbon, SiC vs SiC, and Tungsten Carbide (TC) vs TC. Elastomers include Viton (FKM), EPDM, NBR, Aflas, Kalrez, and PTFE. Custom material specs are available for aggressive or high-purity media.

Legacy OEM seal	Astra replacement
John Crane Type 21 / Type 6A	AS 2100 · AS 110
John Crane Type 502	AS 502
EagleBurgmann MG1 / MG12	AS FBD · AS 2100
Sepco 500 series	AS 2100 · AS 110
Flowserve BX / BXR	AS 128 · AS 110
Chesterton 155 · AESSEAL P04	AS 128 · AS FBD

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