Views: 0 Author: Site Editor Publish Time: 2026-08-12 Origin: Site
Before specifying a double seal, the first question should be whether the service actually calls for one. On clean, non-toxic fluids a single seal is the economical choice and performs reliably. A double seal becomes necessary when the pumped fluid is toxic, flammable or volatile, or when the plant is bound by fugitive-emission limits that cannot tolerate any leakage to atmosphere. EDMA is built for that second category — it is our cost-engineered double-seal line for ANSI centrifugal pumps, providing a genuine secondary containment barrier without paying for over-specified features that sit idle on the pump.
EDMA is a rotary-pusher cartridge seal in a back-to-back arrangement. The two rotating faces are oriented outward and the stationary faces face the intermediate cavity, which is continuously charged with buffer or barrier fluid. Any trace leakage across the inboard face is captured in the barrier fluid rather than released to atmosphere. For the maintenance team this translates into early detection: a minor inboard leak shows up in the barrier system long before it reaches the floor or forms vapor.
The seal faces are hydraulically balanced. In engineering terms, balanced geometry holds the closing force stable across the operating pressure range, which reduces friction heat, lowers shaft power draw and slows face wear. On a pump running continuous duty, these incremental savings compound into a measurable extension of service life.
EDMA shares with our ESMA single seal an external multi-spring layout. Many low-cost double seals place the springs inside the process fluid; on crystallizing, polymerizing or sticky media the springs foul and lock, destroying correct face loading. By locating the springs on the clean barrier-fluid side, we remove one of the most common causes of double-seal failure observed in the field. For fouling-prone services this single design decision protects uptime more than several minor specification upgrades.
There is no universal material set, and incorrect pairing remains one of the leading causes of repeat seal failure we see in service. EDMA is configured to the fluid:
Structure: 316SS
Springs: Alloy 276, for aggressive chemical duty
Faces: carbon, silicon carbide (SSIC) or tungsten carbide (TC)
Elastomers: EPR, Viton, Aflas, Kalrez — selected on temperature and chemical compatibility
EDMA fits the standard ANSI seal chamber and conforms to ASME B73.1 / B73.2 pump dimensions. Shaft coverage is 1.375" to 3.625" (34.9 to 66.67 mm). As a full cartridge unit it is preset at the factory: the fitter mounts the assembly, removes the setting clips and the installation is complete. There is no field measurement of spring compression, no estimation of face load, and no component assembly under the pump.
EDMA supports API 682 plans 52, 53A, 53B, 53C and 54. Pressurized barrier Plan 53 is the standard choice for toxic or flammable fluids; unpressurized buffer Plan 52 with drain applies where a small monitored leakage is acceptable. The seal and its barrier support are one circuit, so the piping plan should be selected on process risk rather than cost.
EDMA is specified across industries running ANSI pumps: chemical and petrochemical, oil and gas, water treatment, pharmaceutical, food processing, hazardous specialty fluids, marine and offshore. Where single-seal failure carries a release risk, the secondary barrier is warranted.
EDMA is rated 15 bar, -20 °C to 120 °C, sliding velocity 20 m/s. It is our economical double-seal line, optimized for moderate-duty standard ANSI pump services. For higher temperature or pressure, or for Durco Mark 3 footprint requirements, our GDMA double seal series is the appropriate selection. EDMA is the correct specification when you need real double containment on a standard ANSI pump under moderate hazardous conditions, without over-engineering the package.
FBU SEALS has manufactured mechanical seals for 18 years and supplies over 50 countries. EDMA draws on lessons collected from thousands of field installations. If you are evaluating single versus double seal, or are unsure which API piping plan fits your fluid, send us your operating conditions — we provide application sizing to confirm the right specification.
Q: What is a double mechanical seal, and when is it required?
A: A double mechanical seal uses two sets of seal faces with buffer or barrier fluid in the intermediate cavity. Any leakage past the inboard face is captured before it reaches atmosphere. It is required for toxic, flammable or volatile fluids, or where fugitive-emission regulations apply and a single-seal failure would create a hazardous release.
Q: How does EDMA differ from the ESMA single seal?
A: EDMA and ESMA are from the same economical product family. EDMA is the double-seal construction; ESMA is the single. EDMA adds the second sealing face and the barrier-fluid cavity for hazardous-media containment. Both use rotary-pusher, external multi-spring design and fit ANSI/ASME B73 pumps on shafts 34.9 to 66.67 mm.
Q: What does "back-to-back" mean on the EDMA?
A: In a back-to-back arrangement the two rotating rings face outward and the stationary rings face the intermediate cavity, which is charged with barrier or buffer fluid. Process fluid passing the inboard face contacts barrier fluid before reaching open air — the accepted layout for hazardous-fluid containment.
Q: Which piping plan does the EDMA require?
A: EDMA is compatible with API 682 plans 52, 53A, 53B, 53C and 54. Use pressurized Plan 53 for toxic or flammable media; unpressurized Plan 52 with drain where limited monitored leakage is acceptable. Select the plan on process risk, not cost — the seal and barrier system are one circuit.
Q: Can EDMA handle abrasive or solids-laden fluid?
A: Compared with seals that wet the springs in the process fluid, the external multi-spring layout gives EDMA better tolerance to moderate solids. Specify SSIC or TC hard faces and maintain clean barrier-fluid conditions. Heavy abrasive services should be submitted to our engineering team for individual review.
Q: What are the pressure and temperature limits of EDMA?
A: EDMA operating limits are 15 bar, -20 °C to 120 °C, and sliding velocity 20 m/s. It targets moderate-duty ANSI pump applications. For higher pressure or temperature, select the GDMA double mechanical seal.
Q: Is EDMA supplied as a cartridge seal?
A: Yes. EDMA is a factory-preset cartridge mechanical seal; no on-site spring adjustment is required for installation.
