Cast iron valves

Cast iron valves are wedge knife and butterfly valves, where the shut-off element (wedge or disc) is cast from grey cast iron, ductile cast iron, or carbon steel WCB. With relatively low production costs and excellent durability, cast iron shut-off and control valves are used in industry, for water mains, natural gas, refined non-aggressive petroleum products and other moderately aggressive environments, as well as bulk products.

Our company “Specialist-P” is engaged in the sale of cast iron valves with DN 50~450, electric and pneumatic actuators for controlling them, as well as related equipment to automate the process regulation. We use WCB due to its advantages in strength and stability compared to grey and ductile iron.

Design of Specialist cast iron valve

Our catalogue presents 6 types of cast iron valves by construction and configuration:

• Flat wedge cast iron valve (knife gate valve):
  • with a rising stem;
  • with a linear pneumatic actuator;
  • with a non-rising stem (on request);
• Cast iron butterfly valve (flanged or wafer):
  • with an electric actuator;
  • with a manual drive;
  • with a pneumatic actuator.

Cast iron knife gate valve with rising stem

The type of knife gate valves with rising stem in our catalogue is represented by the series SCBF-PZ673X-10JC with wafer mounting method and handwheel for control.

Principle of the rising stem

Rising stem is a design in which during the opening of the valve with a handwheel, the threaded part of the stem rotates and extends from the body, making it possible to immediately visually determine the position of the wedge. An additional advantage of the movement of the stem outwards is the better tightness, absence of thread contact with the working medium, and the possibility to lubricate it without disassembling the valve.

Cast iron knife gate valve with pneumatic actuator

SCBF-PZ673X-10JC, the same model, is produced as a knife gate valve with a linear pneumatic actuator. It is controlled by compressed air from a compressor, which can generate significant forces and control very heavy gates.

Standard knife cast iron valves with a pneumatic actuator operate in the “open-close” mode and allow very quick shutdown of the working medium flow. If necessary, we can produce non-standard multi-position pneumatic cylinders and with stroke regulation to provide additional intermediate positions.

Features of Specialist cast iron valves construction

Reinforcing the rubber seal of the wedge (knife gate valves)

Our company “Specialist” uses the best practice when NBR, EPDM, or Viton is cast on the surface of a steel core. After this, the seal is placed around the entire seat perimeter under the knife. This allows the elastic and soft rubber to be stiff enough to retain its geometry and integrity even after many cycles of operation, and this is crucial to maintaining high pressure tightness of the shut-off valves.

Cast iron valve with a rubberized wedge or disc

Cast iron valve with rubber-coated wedge (option) is capable of providing a longer service life and a high class of shut-off valve tightness (class “A”). This is achieved through the vulcanization of NBR, EPDM, or Viton on the cast iron knife. This not only provides it with a chemical-mechanical bond but also enhances the rubber characteristics.

Butterfly cast iron valves of the SV-BV2 series with a rubberized wedge are used for abrasive bulk products, as well as food products.

Why the wedge or disc WCB is better than grey or ductile cast iron

Grey cast iron (ASTM A126 Class B) is the cheapest for manufacturing valves. However, it is rarely used for industrial valves due to its brittleness – it cracks upon impacts, temperature fluctuations, is unable to withstand pressure.

We do not recommend buying cheap cast iron valves where the grade is not specified, as they are most likely made from crack-prone grey cast iron.

Ductile cast iron grade ASTM A536 is produced using a more complex technology. It is less brittle and has better corrosion resistance. However, to achieve a truly reliable cast iron valve, substantial thickness is required, which affects the weight of the valve.

In some cases, ductile cast iron, cheaper than WCB, has an advantage – systems of Ukrainian cold water supply with chloride content to domestic users, wherein the ability to absorb vibrations is useful as sound insulation. Depending on the grade, ductile cast iron can approach WCB characteristics but CANNOT surpass the thermal resistance of cast carbon steel and loses under high pressure.

WCB grade ASTM A216 WCB is often referred to and sought as cast iron, though technically correct to call it “cast carbon steel”. Even without alloying, WCB outperforms cast iron due to its ability to withstand high pressure and temperatures. WCB is used for steam and hot water under high pressure in boiler installations and manufacturing. Most international standards for high-pressure gas pipelines also require the use of steel (e.g., API 6D for mainlines).

Packing materials for cast iron shutters.

We offer various rubber seals:

• NBR, with good resistance to cold water, petroleum products, many fuels, and lubricants, fats, and some solvents. Moderate thermal resistance, recommended operating range from -20 to +80°C. Not resistant to oxidizers, UV radiation.
• EPDM, more suitable for hot water, has resistance to most weak organic acids, alkalis. By default, we offer affordable s EPDM seals with sulfur vulcanization and a heat resistance of up to +95°C.

If you use steam, crude oil, and oil products with a content of

• FKM, also Viton® with higher resistance.
• PTFE this is the more expensive and most resistant polymer seal, with high inertness to acids, alkalis, petroleum products.