Hydrostatic Gas Lubricated Mechanical Seal Characteristics

Gas lubricated mechanical seal,also named as a gas face seal or dry gas seal,can be used to seal gas or liquid media.With the development of economy and society,the demand to the gas lubricated mechanical seal performance becomes higher and higher.How to solve the problem of seal stability on low speed machines becomes popular at home and abroad. Aerostatic gas lubricating mechanical seal technology has good seal performance on low speed mechines,which has attracted the attention of many researchers.Aerostatic gas lubricating mechanical seal is a new kind of seal in which the aerostatic gas is used to separate the seal faces resulted in non-contact between faces.The gas control equation has been solved by Finite Difference Method in this paper.The influence of the different structure parameters and operation parameters upon the gas pressure distribution between faces,open force,gas stiffness and gas leakage rate has been studied thoroughly. Further more,gas film and stationary ring vibrational regulation when mate ring bears axial tiny vibration has been analyzed.The main contents and conclusions are as follows:1.The existing gas flow control equation of aerostatic gas lubricating mechanical seals has been programmed by Visual Basic.Three-dimensional distribution of gas film and gas pressure has been showed by invoking the Matlab program.2.The influence of structure parameters(The depth of grooves,Orifice restricted radius, Grooves size)and operation parameters(Media pressure,Gas pressure in external source, Mate ring rotate speed)upon seal performance(Including:face open force,gas stiffness, gas leakage)has been analyzed by the program.The results are as follows:(1)The influence of grooves depth upon seal performance is not significant as to grooves depth range of 3-15 microns investigated in this paper.(2)Open force and gas stiffness are large and the gas leakage is low when the restricted orifice diameter is 0.15mm.The film stiffness decreases rapidly though the open force increases when the restricted orifice diameter is larger than 0.15 mm.(3)The seal performance is good when grooves length ratio is between 0.6-0.8 and width ratio is about 0.6.(4)Open force will increases and gas leakage of the external gas source will decreases when the media pressure rises,but gas stiffness decreases now.(5)Gas pressure of external gas source has a great effect on seal performance.The good seal performance can be achived by regulating the gas pressure of external gas source.Gas stiffness and open force increases when gas pressure of external gas source increases,but the gas leakage increases quikly.(6)The influence of the mate ring rotation speed upon the seal performance is very small.The influence of the mate ring rotation speed can be ignored.3.The influence of face shape of roughness,waviness and radial taper upon seal performance has been analyzed in this paper,and the analytical method was programmed by VB.The calculational results are as follows:(1)Open force and gas stiffness increases when radial direction roughness increases,the results exactly opposite when only consider surrounding direction roughness.(2)Seal stability increases when seal face appears positive taper or negative taper,but gas leakage to the media side is large when positive taper appears on seal face and gas leakage at media side is low when negative taper appears on seal face,so it should avoid the positive taper appears.The negative taper should not be larger than 0.03 degree;otherwise the two seal rings may contact and the wear will be serious.(3)Th gas film thickness should be revised when considering the circumeritial waviness on seal face.The open force and the gas stiffness are large when the start angle of cosine of the circumeritial waviness is 180°whose starting point is at the middle point between two grooves,but the gas leakage is large now.4.The vibrational regulations of the gas film between the seal rings and the stationary ring have been investigated under axial tiny vibration.The results are as follows:(1)The displacement of the gas film thickness is lower than 0.3 microns though the axial swing of the running rings is 300 microns.The stabile gas film can be got and the non-contacting operation can be stable.(2)Gas film swing has increment when spring stiffness increases, but the change quantity of swing is very low.(3)Gas swing will decrease much when gas stiffness increases.(4)The influence of the stational ring quality and seal face area upon the gas flim swing is very small.