High temperature control valve refers to the valve working temperature higher than 450 ℃.The high temperature can be divided into 450 ~ 600 ℃ and 600 ~ 700 ℃, 750 ℃.

1 What are the main issues usually involved with the high temperature control valve?
Serious heat expansion and cold contraction, so that the guide clearance, control valve plate rotation clearance become overfilling due to expansion and reduce, and get stuck.At high temperature situation, the creep of materials leads to the deterioration of mechanical properties of materials.

2 How to choose the material of high temperature control valve body and inner part from the consideration of thermal strength?
Used for above 450 ℃ environment, in the temperature and pressure must be considered  on the material mechanical strength during the design and selection, the influence of such as boiler feed water system and bypass system under the condition of high temperature overheating, High temperature control valve body and trim material is not applicable for common material.Therefore, more durable materials must be used.General materials can be used the highest temperature of 500 ℃ or so.On the occasion of higher than 538 ℃.The body usually uses chromium molybdenum steel.On the occasion of the maximum temperature of 1035 ℃ or so, usually choose SUS310S stainless steel, carbon content and materials must be controlled between 0.04% ~ 0.08%.Lining for higher temperature, the recommended non-metallic refractory material can be used in the high temperature of 1200 ℃ occasions or special high temperature resistant, high strength alloy (such as engine combustion chamber, high temperature resistant high strength alloy can be directly used in 1000 ℃ high temperature occasion.)

3 From the consideration of hot expansion and cold contraction, how to adopt measures to prevent leakage from the structure? 
The valve seat sealing method can be used to prevent leakage.When the temperature is as high as 750, the threaded seat causes leakage at the sealing surface and threads connected to the body and erodes the threads, resulting in a risk of seat drop.The seat should be considered for sealing to prevent looseness and shedding in case of this combined fault.

4 For different operating temperature ranges, how to select the high temperature control valve?
For operating temperature range 450 ~ 600 ℃, can choose the common structure high temperature control valve.For the operating temperature range of 600 ℃ above, the current domestic high temperature control structure of butterfly valve, valve lining refractory material, the aggregation structure is very heavy.A better method should be directly with high strength alloy, the alloy can be directly in 900-1000 ℃ temperature range, such as the engine combustion chamber will choose this kind of material, they are not only the temperature resistant performance is good, and good strength properties.With this material, large diameter butterfly valve can be used, medium and small diameter ball valve can be used, such as eccentric half-ball valve. It differs from other products in the following three features:
1. High-temperature and high-strength alloy for materials;
2. Sealing problem of upper and lower cover.
3. Problem of high temperature filler.