Ammonia globe valve
Ammonia globe valve
Ammonia is an essential raw material for the manufacture of nitric acid, ammonium salt, and amine. Ammonia is a gas at room heat and can be liquefied under pressure. Most elements such as Stainless steel, Aluminum, Lead, Magnesium, Titanium, etc. have superior corrosion resistance to ammonia gas, liquid ammonia, and ammonia water. Cast iron and carbon steel also have excellent corrosion resistance to ammonia gas or liquid ammonia, the corrosion rate is generally less than 0.1mm/year, so ammonia production and storage equipment are commonly made of steel from the aspect of cost.
The check valve, globe valve, ball valve, and other valves can be used in the ammonia and liquid ammonia piping method. These devices bring the gas pressure down to a safe level and pass it through other valves to the service system. Among them, the most generally used is the globe valve. Ammonia globe valve is a kind of force-sealing valve, that is, when the valve is closed, the pressure must be utilized to the disc so that the sealing surface is leak-free.
When the medium enters the valve from below the disc, it is important to overcome the friction of the stem and packing and the pressure from the medium. The force of valve closure is more prominent than that of valve opening, so the diameter of the stem should be large or the stem bending. The flow of self-sealing ammonia gas globe valve is regularly from top to bottom, that’s the medium into the valve cavity from the top of the disc, then under the pressure of the medium, the force of valve closing is small and the valve opening is big, the diameter of the stem can be correspondingly decreased. When the globe valve is open, when the initial height of the disc is 25% ~ 30% of the nominal diameter, the flow has reached the maximum, indicating that the valve has reached the fully open position. Therefore, the fully open state of the globe valve shall be determined by the tour of the disc. So what are the features of globe valves for ammonia application?
Copper reacts with ammonia gas and ammonia water to form solvent complexes and produce dangerous stress corrosion cracking. In the ammonia atmosphere, even trace quantities of ammonia can cause stress corrosion in the atmosphere. Pipes made of copper and copper alloy are generally not suitable for ammonia forms.
Ammonia globe valve is an ono-rising-stem cone design associated with the common globe valve. Its sealing cover is mostly Babbitt reduction and the valve body is made of stainless steel CF8 or high-quality carbon steel WCB to be used to the maximum conditions, which can be contrary to ammonia corrosion, low-temperature protection to -40℃.
The tongue and groove face design of the flange connection ensures reliable sealing performance even when pipeline pressure fluctuates. Multi-layer PTFE (PTFE) or Babbitt alloy sealing material and a composite soft packing made of PTFE+ butanol + spring) assure that the valve packing box is free of leakage through the service life. PTFE plain gaskets, stainless iron + graphite wound gaskets, stainless steel + PTFE wound gaskets are also approved for ammonia valves.
The handwheel of the ammonia globe valve is commonly painted yellow to distinguish it from valves for other applications. In addition, vertical check valves and help control valves are also possible for ammonia applications. Their discs rise and fall depending on the differential pressure of the fluid and their weight, automatically stopping the medium against the current and protecting the upstream equipment, suitable for most ammonia tanks on the horizontal pipeline.