Edwina Dorsey Valves April 14th, 2019 - 12:34:54
As a rule customarily, the sealing face for the low-pressure valve mostly applies the brass or brozen. The sealing faces of the high or middle-pressure valves are made of stainless steel. If the valve has high requirement for the temperature or pressure, cobalt base alloy is used as the main material of the sealing face. What's more, the polymeric material is widely used in the valve field. For example, PTEF material is applied into the seat of ball valves, different rubber materials for seal packing ring of the butterfly valve and septum of the diaphragm valve. All in all, the sealability of these materials is better than that of metal in the available temperature range.
Among all the above mentioned considerations, it is rather necessary to talk about the actuator and positioner design. These two must be considered together. The combination of them affects the static performance (dead band), as well as the dynamic response of the control valve assembly and the overall air consumption of the valve instrumentation.
More recently, on the PEX plumbing and radiant heating networks as brass fittings water shutoff dominated by two products: "valve cork entrance omental tapered Threaded Brass Ball Valve BVT012D" and "Sweat Brass Ball Valve BVS012D". Passport service life of tube-omental valve - 8 years, the average life-at least 1500 cycles, time to failure - at least 400 cycles. In fact, these valves after 40-50 cycles begin to be capricious: cotton gland packing into a brown porridge, soaked in water, and the cone stop tube, originally friction to the body under the influence of abrasive solids and sludge sediment in the water begins to hang out in the body, passing water in the closed position. If you also take into account the extremely high coefficient of local resistance plug valves (3,5-5,7), it is not surprising that plumbers often just throw the locking cap, leaving the body dubious backdrop of the pipeline.
Valve response time is another important factor for us to consider. For optimum control of many processes, it is important that the valve reach a specific position quickly. A quick response to small signal changes is one of the most important factors in providing optimum process control. Valve response time includes both the valve assembly dead time, which is a static time, and the dynamic time of the valve assembly. It is important to keep the dead time as small as possible. Dead band, whether it comes from friction in the valve body and actuator or from the positioner, can significantly affect the dead time of the valve assembly.
In most places right now, the non-rising stem as well as the rising stem valve are two of the commonly used valves. The valve is known as the rising stem is recognized through its string shaft that is turned by a handle located in the middle. The shaft is raised up when the handlebar is revolved. It rises when the valve is released and when the valve is shut, it drops down. Therefore, it is easier to know the valve shaft's length placement above.
In standard valves, when it is given a command to open to a certain point, there is no feedback to verify that the valve has opened to that position. With a valve positioner, the command is given and the valve positioner reads the opening, verifying the position and readjusting until it gets it to the exact position needed. This allows for great precision in the adjustment.