In the evaporative and crystallization technology process ,such things happens frequently .That is valve can not open as the medium gathering at the bottom of tank , so it lead to the medium can not be discharged . To solve this problem , the only method is flushing the blocked valve by high pressure water or high temperature steam . it is time wasting and inconvenient. 
How to solve this problem in valve field ？ Now a new type of valves have been studied , that is tank bottom angle valve (disc opening into the tank type ) ,working as the special discharge medium valve ,can solve the problem better . The outlook and application is described as the following picture :
    
The above picture is tank bottom angle valve installed at the CuSO4 crystallizer to work as the discharging medium .
Tank bottom angle valve (disc opening into the tank type) is suitable to discharge and sampling the medium at the bottom of crystallizer . It usually welding at the bottom of tank or other vessel by the flange of the valve . The disc of tank bottom angle valve is designed as the flat type , valve body type is Y type , the valve disc is classified as open up and open down according to different working style . The sealing ring is set inside of the valve body ,and hard alloy is overlaying on the sealing surface of the disc , the sealing type is designed as liner sealing to have a reliable sealing and anti-scaling function .
So the engineer can select tank bottom angle vale according to your working situation on site in the Design of crystallization system.