Amie Brewer Valves April 14th, 2019 - 12:24:10
A valve is a device on many instruments which redirects the airflow into a separate section of tubing before returning to the main tubing. While depressed, this "extra" tubing is in use, therefore increasing the length of working tubing and lowering the pitch. On almost all modern horns, the valves work in the same way: the 2nd valve lowers the pitch by one half step, the 1st valve lowers the pitch by one whole step (two half steps), and the 3rd valve lowers the pitch by one and a half steps (three half steps). If there is a fourth valve, it will lower the pitch by two and a half steps (5 half steps).
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.
Swagelok produces a variety of Check Valves to meet every need. All Check Valves are factory tested for crack and reseal performance with a liquid leak detector. Check Valves with fixed cracking pressures are cycled six times prior to testing. Every valve is tested to ensure it seals within 5 s at the appropriate reseal pressure. Check Valves with adjustable cracking pressures are tested at two pressure points. Every Valve is tested at a low-pressure setting and at a high-pressure setting, and all must seal within 5 s at the appropriate reseal pressure.
The 4th valve solves some problems and adds others. The 4th valve adds 38.08 inches of tubing in the case of our 100" instrument. This is a substitute for the 1-3 combination as the 4th valve has the correct amount of tubing to be in-tune. Likewise, the 4-2 combination produces a pitch more in-tune than 1-2-3 as it only lacks about 2.54 inches of tubing from the theoretical length. So this is great, now we have all of the seven common combinations relatively in tune right? This is true, however, this 4th valve grants access to a range which three valve instruments cannot reach. When using combinations with the 4th valve, euphoniums can reach notes such as D below the staff, a note which is not possible using three valves. Now we get to the curse of the 4th valve. When using the 4th valve in combination with other valves to reach these low notes, the problem described above compounds on itself even further. To lower the pitch a whole step after depressing the 4th valve, 19.02" must be added in addition to the length of the 4th valve. Generally, the first valve would lower the pitch by a whole step, but remember the length of the first valve tubing? 13.77 inches. Again, this problem compounds as more valves are depressed. Using the 1-2-3-4 combination, which using the half-step definitions of the valves, should provide a B natural a half step above pedal Bb. However, the length of tubing for a low B natural is a whopping 203.38 inches! The combined length of all four valves only equates to 173.22 inches... Thats only enough for a slightly sharp C! Thats right, that means that B natural is not possible (without lipping from the performer) on a non-compensating 4 valve euphonium.
The formula for the theoretical length of tubing, TL, needed to lower a set number of half steps, x, for an instrument of length, L, is TL = L (16/15) ^ x. Example: 100" instrument lowering 3 half steps: TL = 100(16/15)^3. TL = 21.36.
Ball valves are usually quarter turn valves (as we turn the lever by 90 degrees to start or stop the flow) and use a hollow, perforated and pivoting ball that is also called as a floating ball. It is through this valve that the flow of fluids takes place. When the lever or handle is turned to 90 degrees, the hole of the ball gets aligned with the pipe opening and starts the flow. When again the lever is turned by 90 degrees, the hole turns around and the ball blocks the opening of the pipe thus causing the flow to stop.