Chemical Seals form a barrier between the instrument and the pressure medium. Their main uses are to protect against blockage of the instrument’s pressure entry, and to protect against corrosion.

Protection against blockage: The pressure medium may contain solids, or it may be highly viscous. For this application, as large a bore as practical should be used. 50mm Table 1 000 flanges, or 2” threaded connections, make a good choice for conventional seals. Extended nose designs, which protrude into the pipe nozzle and place the diaphragm flush with the tank wall, are expensive, but suitable for the worst tank applications where nozzle blockage is likely. In-line designs may be used for slurry pipe-line applications.

Protection against corrosion: The diaphragm is typically 75μ thick, and must be highly resistant to corrosion by the pressure medium. The process connection, which is much thicker, can tolerate much heavier corrosive attack. There is no universal offering. Even tantalum, which resists so many boiling acids, is attacked by something as ordinary as caustic soda. If you are unsure of what to use, tell us your conditions, i.e. temperature, concentration, degree of aeration, and we will check for a match against our extensive database

Available Designs:
Our standard design (SC) is based on a mechanically clamped diaphragm. This design was originated to allow us as a South African company, to match and even exceed the offerings of the larger multi-nationals. Manufacture is based on a number of blanks, which are investment cast, allowing virtually any air-castable material to be used. This procedure makes it possible to provide very competitive pricing on the less common materials, in relatively small quantities, since we buy less material, and machine less away, thus making a double saving.

We believe our top housing, or instrument flange, is unique, in that it offers male connections when required, which eliminate the additional leak-paths caused by adaptors.

For screwed connections to 1” male or female, our stock process connection blank is machined to customer’s requirement, and has a built-in hex for fastening. There is no need to build a “Christmas Tree” of adaptors, we will make the seal match the connection on the plant!

To retain a full size diaphragm, 63mm active diameter, in small flanged connections, and to allow through bolting of the flanges without resorting to blind tapped holes, we use the double flange design shown above.

The diaphragm is usually sealed by means of a metal-to-metal joint, thus eliminating soft seals, and allowing use to 300ºC.

The advantages of this design are simple field replacement of diaphragms, and a flexibility in choice of diaphragm and process connection materials independent of weld compatibility. Click here for data sheet.

High Pressure Design:
The standard design is rated to 4 MPa, and can be extended to 10 MPa. For higher pressures, our HW range uses welded diaphragms, mated with a diaphragm bed, which provide high overload, survivability in the event of loss of fill, and the ability to operate to 60 MPa.

Flush Welded Design:
We can build flanged connections with flush diaphragms, again provided with diaphragm beds, in a variety of sizes and materials. Details on application.

Materials:
For process connections, we usually keep in stock the following, although other materials may be available if required:

16 stainless steel is the lowest cost option for general purpose use.
Aluminium bronze is useful for many applications where stainless is unsuitable, eg dilute sulphuric acid.
Monel 400 is used in applications like HF acid.
Alloy 20 is useful on sulphuric acid in most concentrations.
Hastelloy B is the best metal for hydrochloric acids.
Hastelloy C has good general resistance to strongly oxidising media such as chlorine

We stock diaphragms in the following materials. Once again, other materials may be available on request.:
316 Stainless Steel: The industry standard for general purpose use.
Tantalum: An extremely expensive material, inert to most corrosives.
Titanium: An very useful material, with excellent resistance to most organic products and chlorides
Inconel 600: A nickel chromium iron allow with excellent resistance to chlorides and caustics.
Hastelloy C276: A nickel chromium molybdenum alloy with excellent resistance to a wide range of corrosives.
Monel 400: A high nickel alloy with excellent resistance to brines.
PTFE: Used as a liner, usually with stainless steel backing.
Silver: Expensive, but often useful for niche applications.

As a service, we provide information on pipe diameters and flange sizes. This information is intended for help in identifying connections, and Blanes Pressure Solutions takes no responsibility for the correctness of such data.

Pipe Sizes

Flange Size