QPF-F50-type pneumatic balance valve, also known as the main pressure reducing valve, used in pneumatic circuit, the compressed air pressure value is adjusted so that the set pressure value is nearly constant. The valve is pressure-relief valve combination. When the outlet pressure is lower than the set pressure, it acts as a pressure regulating valve to increase the pressure to the set pressure. When the outlet pressure is higher than the set pressure, the relief valve acts as a relief valve to reduce the outlet pressure to the set pressure. In order to ensure that the export pressure has always been stable at the required set pressure. Because of the valve at the same time has the characteristics of pressure regulating valve and relief valve, it can replace the pressure regulating valve and relief valve at the same time work, than in the gas system separately set pressure regulating valve and relief valve, the system is simplified and compact . At the same time, the pressure difference between the pressure regulating valve and the relief valve is also eliminated to ensure that the air pressure in the system can be more accurately regulated and stabilized at the required set pressure value. The valve belongs to the pneumatic pressure relief relief valve with outlet pressure feedback. It is normally closed when no pilot signal is input (as shown in Figure 1). Figure 1 QPF-F50-type pneumatic balance valve When the pilot air compressed air into the B cavity, the valve began to work. The level of the output pressure is controlled by the pressure entering the pilot port CP and the outlet pressure is set by adjusting its pressure. The compressed air entering the control chamber B from the port CP pushes the piston 8 together with the spool 6 thereon axially upward to overcome the force of the spring 7 to compress it. After the relief valve port (ie, the upper end face) of the valve core 6 is completely contacted with the bottom surface of the valve cover 3, the output and overflow passages are blocked. The piston 8 continues to move up and the valve core 6 pushes up the valve cover 3 in the axial direction and compresses the spring 1 on the valve cover 3. The pressure regulating valve port is opened and the input chamber and the output chamber are communicated with each other. Pressure regulator into the output cavity, the OUT port output. Compressed air from the output chamber enters the A and C chambers via the 2 gas lines on the valve body. The pressure of the gas in the three chambers is the same. When the output pressure is lower than the set value, the force on the lower side of the piston 8 is greater than that on the upper side, the piston 8 moves upward and the valve cover 3 is pushed up so that the pressure regulating valve port is enlarged and the pressure of the pressure regulating valve port enters the output chamber Air flow increases, the pressure of the output chamber will rise. When the output chamber pressure reaches the set value, the pressure on the upper and lower sides of the piston 8 is in equilibrium, the piston 8 stops moving up, and the opening of the pressure regulating valve port remains unchanged. Output pressure and flow of compressed air output remain stable. When the output pressure is higher than the set pressure, the force on the upper side of the piston 8 is greater than the lower side, and the valve cover 3 and the piston 8 move downward together to reduce the opening of the pressure regulating valve port and enter the output chamber through the pressure regulating valve port Of the gas decreases, the pressure of the gas in the output chamber decreases. If the pressure of the output chamber is still higher than the set value at this time, the piston 8 will continue to move down until the pressure regulating valve port is fully closed. The force of the spring 1 on the valve cover 3 no longer acts on the piston 8 via the valve core 4 but presses the rubber pad on the underside of the valve cover 3 tightly against the pressure regulating valve port and the passage between the input chamber and the output chamber Been cut off At this time, if the output pressure is equal to the set pressure value, the piston 8 stops moving. Pressure is set at this time in the pressure relief valve port and relief valve port closed at the same time, the valve is in static equilibrium outlet pressure. If the output pressure is still higher than the set pressure value, the piston 8 continues to move downwards, the relief valve port ie, the upper end surface of the valve core 6 is separated from the bottom surface of the valve cover 3, the output chamber is communicated with the overflow chamber, Relief valve port through the EX port discharge. As the pressure in the output chamber drops, the pressure in chamber C will also drop at the same time. The pressure on the lower side of the piston 8 is higher than the upper side, so that the piston B and the valve core 6 move axially together to gradually close the small relief valve port degree. When the output pressure reaches the set value, the overflow valve port and valve cover 3 bottom fully fit, the output chamber and the overflow chamber between the channel is cut off, overflow stop. At this point, the relief valve port and pressure relief valve port closed at the same time, the valve is stopped in the gas flow static equilibrium. As the air pressure on the upper and lower sides of the bonnet 3 are in equilibrium with each other, no matter how the pressure in the air inlet (IN) fluctuates, the pressure balance in the valve can not be affected, so that the outlet pressure can be ensured to be stable at all times In the set value, the valve has good pressure characteristics.
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