Metal Bellows Mechanical Seals Design Features
1.  Wide service range from cryogenics to heat transfer liquids and corrosive chemicals.
2.  Long MTBR(Mean Time Between Replacement) since there is one moving part, metal bellows.
3.  Flexible bellows construction eliminates seal hang-up due to solids or dirt in pumpage.
4.  Metal sealing wedge eliminates temperature restrictions of elastomers or plastics.
5.  Built-in hydraulic balance eliminates step in shaft or sleeve.
6.  Available for either inside or outside mounted.
7.  Stabilizer tabs prevent possible damage due to vibration and excessive shaft run-out.
Metal bellows mechanical seals will not fret the shaft or sleeve because it has no dynamic (sliding) 0- ring. All pusher seals (seals with springs) have dynamic 0-rings. This means that you can mount either metals bellows mechanical seals directly on the shaft and save the cost of sleeve. Because the bellows that act as spring does not have to overcome 0-ring friction drag, as does the  pusher seal, the spring load can be lighter than in the pusher seal design. Some common pusher seals have spring loads about 50 psi, while the metal bellows load is approximately 25 psi. This can result in up to 50% decreased seal face wear rate. The metal bellows produces even face loading, superior face tracking and less frictional heat.

Metal bellows mechanical seals feature a metal bellows core made of one of several types super alloy or steel.   The most common are AM350, Inconel 718 and  Hastelloy C-276.   Usually with Alloy 42(Carpenter 42), Stainless Steel (SS 316) end fittings permits these metal bellows mechanical seals to be used for services beyond the range of mechanical seals with elastomer as secondary sealing element.
Typical applications include: cryogenics, heat transfer fluids, severe chemicals, slurry and corrosives at temperatures from —350° to +800°F (—212° to +425°C) with standard seal construction.

Mechanical Seals with metal bellows design has several obvious   advantages compared to pusher or   elastomer bellows design. Some of  them are as follows:
      – Dynamic o-ring is eliminated. Superior performance, no hang up or shaft fretting.
      – Hydraulically balanced seal. Allows seal to handle more pressure without heat building up.
      – Self cleaning. Centrifugal force throws solids away from seal.
      – Fits small seal envelope.
      – Available in metric and imperial sizes.
      – Bellows spring design allows 360 degrees even face closing force.
      – Various choices of seal face, elastomer and metal materials to suit demandingapplications.
      – Solid single piece construction.

METBEL  metal bellows mechanical seals  have dedicated our resources to promote and   develope design to cope with customer’s demanding application. Please go to our Product   page to explore our metal bellows that  suitable to your application. In case you  have any questions, suggestions, comments or can not find what you are looking for, please feel free to  contact us. We will reply in next business day.

Bellows technology of the twentieth and twenty-first century is centered on metal bellows. These high-technology products bear little resemblance to the original leather bellows used traditionally in fireplaces and forges.

There are two types of metal bellows – formed and welded. Formed bellows are produced by a variety of processes, including mechanical forming and hydroforming. The welded bellows is manufactured by welding individual formed diaphragms. The pro and con comparison between the two (formed and welded) bellows generally centers around cost and performance. Formed bellows generally have a high tooling cost, but may have a lower piece price. However, the formed metal bellows has significantly lower performance characteristics. Welded metal bellows are produced with a lower tooling cost and maintain significantly higher performance characteristics. Another area of comparison is in metals of construction. The formed bellows is limited to metals with high elongation characteristics, whereas metal bellows may be fabricated from a wide variety of standard and exotic alloys, such as stainless steel and titanium, as well as other high-strength, corrosion-resistant materials.

Welded bellows can be fabricated from a greater variety of exotic metals and alloys, whereas formed bellows are limited to alloys with good elongation – brass being a prime example. Welded bellows are not fabricated from brass because of its fundamentally poor weldability. Other advantages to welded bellows include compactness (higher performance in a smaller package), ability to be compressed to solid height with no damage, resistance to nicks and dents, and dramatically greater flexibility.

The welding of metal bellows is a microscopic welding process, typically performed under laboratory conditions at high magnification.

Welded metal bellows are used in a wide variety of products and marketplaces, including medical applications like implantable drug pumps, to industrial seals, sensors and actuators, to aerospace applications such as altitude sensors and fluid management devices (accumulators, surge arresters, volume compensators, and fluid storage). Welded metal bellows are also found in space applications, providing reservoirs with potable water as well as accumulators to collect waste water.

Q: How can I know what model of mechanical seal that I am using?
A: You might compare your OEM’s drawing with other vendor’s drawing. Actually, most popular model have the same design but they are called as different model.

Q: How can I switch to try another vendor’seal if I don’t have the drawing?
A: You just tell them informations of your stuffing box dimension and your application they will choose an appropriate seal for you.

Q: What service period is considered good life for a mechanical seal?
A: If you mean longest service life, as far as it concerned should be good. Actually, it has to syncronized with your preventive maintenance plan. Normally, seal will be damaged when you  disassembly you equipment for maintenance. It is worthless to have seal that can stand for  5  years while you have maintenance plan for every 3 years.

Q: Why do most seals fail prematurely?
A: Survey of pump populations carried out over a period of years in the USA suggest that  the basic causes of seal failure and their relative importance stated that only 10% of seal failure  are caused by the seals themselves. The rest are operating problem, mechanical difficulties,  faulty fluid circuit design and miscellaneous causes.

Q: What are the most common causes of component damage?
A: The weakiest point of seal is secondary seal the second weakiest is spring. So common causes of component damage is incorrect material selection especially for tough application.

Q: What are the most common causes for the lapped seal faces to open?
A: Hang up of secondary seal, springs or metal bellows.

Q: Do seal faces have to be lubricated? Can they run dry?
A: No need to be lubricated. The process fluid itself will act as lubricating fluid. But if you  use in high pressure application without balanced seal closing force, they can run dry.

Q: Do seal faces have to be kept cool?
A: Seal face will have longer life if it be kept cool. But normally seal face can stand for  300- 600 degree celcius depend on type of material.

Q: When should you use two hard faces?
A: When your fluid is contain solid particle. For example, in waste water treatment process  we use silicon carbide with silicon carbide seal face.

Q: Why not standardize on two hard faces?
A: In some cases like light duty of clean fluid, it is too costly. So why pay more.

Q: Do seals have to leak?
A: Yes, sooner or later. So managing seal utilization is quite challenging job. Actually, all  mechanical seal is leaking while running. But it is very little amount that you can not see it.

Q: Why do most original equipment seal designs frett and damage the shaft under the  dynamic elastomer or spring loaded Teflon?
A: Cost of seal is lower. You can change to metal bellows design that eliminate this problem  but cost is a little bit higher. To check out advantages of metal bellows mechanical seal, please  click here.

Q: Do you have to flush most slurry applications?
A: Have flushing is better. But now we have innovative design that can have no flushing.  Need more details, please contact us.

Q: When my metal bellows seal fails because of breakage at the plates, the break is  always near the end fittings and never in the middle of the bellows. How is that  explained?
A: To much torque load at the plates, or bellows diaphram, and the plates can not stand for.  It might  caused by too closed working length set up, high viscosity fluid or shock load when  starting equipment.

Q: Every time I remove a rubber bellows seal from my pump it is stuck to the shaft.  Why?
A: Your operating temperature might be too hight or bellows slipped while operating that  cause friction and heat. So check tolerance of your bellows and shaft and material of bellows  that suitable for your operating condition.

Q: Why does my outside mounted seal make a whistling sound?
A: Seal faces might be running dry caused by too close working length setting up. It might  burn your seal faces in short period as well.

Q: Do I need the new gas seal if I want to seal fugitive emissions?
A: As you might know, fugitive emission come out from seal face while running. Gas seal is  designed for zero emission to the atmosphere. As the choked gas whose pressure is higher than  pressure of transferred fluid is input to block emission. Need more details, please contact us.

Q: What is a cartridge seal?
A: A self-contained mechanical seal that can be bench assembled and fitted directly without  the need for further adjustment.

Q: Why not mount the seal outside the stuffing box and then dirt and solids will not get  into the springs and sliding parts of the mechanical seal?
A: Good idea. But there is some disadvantages that seal faces cooling is poor and it effect  seal life. In high speed rotating case, seal faces will be burned out in few minutes.

Q: Why not standardize on Teflon as the preferred rubber part in a mechanical seal?
A: Actually. Teflon is plastic, not rubber. Its flexibility is poor. So we prefer to use rubber.

Q: Why should you not use stainless steel springs or stainless steel bellows in  mechanical seals?
A: Yes, we use in some case for light duty. Its cost is much lower than super alloy.

Q: If I touch the lapped faces, are they ruined?
A: No, if you clean it before using with soap water and clean cloth.

Q: Should I be using split mechanical seals?
A: Split seal is useful when you have an equipment that has large and long shaft. It is very  convenient to install split seal and save much time.

Q: Is it O.K. to have a third party rebuild my mechanical seals?
A: There are 2 things that concerned. Cost and reliability. Choose one that you think you  can relia on and fast service. No need to talk about cost. It must be competitive.

Have more questions. Please send them to support@metbel.com
We will reply in next business day.