Valve alignment is a very important factor inthe proper set-up of a professional brass musical instrument. Air flow andresistance are two factors which play a big part in the ease with which ahorn responds.By having the valves properly aligned, a horn will reveal itstrue colors.
Due to the way in which valves are constructedand assembled there are natural inconsistencies which occur. The liners (tubeswhich run through the "Pumps",or valves) may often times be malformed duringthe ballizing process. To expand the liner to the proper diameter betweenthe holes drilled in the pump(ports in valve), several balls, attached tolong rods must ,while spinning,be pushed through the liner material .Theirregular shape of the passage between any two holes through which aliner passes in the pump can cause the tubing to wander during the ballizingprocess. You will notice this effect by looking at the port which connectsthe tuning slide tubing to the third slide upper tubing on a trumpet pistonvalve.Many manufacturers have engineered this problem away as much as possibleby correcting the angles, but there is not enough room to make the tubingcompetely straight and smooth.Tooling(sizing balls) that is worn will alsocause the liners to have irregular sratches on the surface of the liners.
The connecting tubes, or knuckles, on the valvecasing are hard soldered or brazed in place. It is important to make surethat each tube is properly soldered. During the brazing process(applicationof hard solder to connecting knuckles)the casing is warmed to around 1100degrees causing severe, in some cases, prostration.When cooled, the casingmaintains some of the tension casued by prostration due to the extreme heat.Thisis most apparent at the edges of the inner passages. Many instrument makershave the forsight to remove a small amount of material around the edge ofthe tubing inside the casing before fitting the valve.This helps to preventany possibilty of the valve sticking because of movement that occursin the case tubing caused by the heat produced while playing. Many hornswill have problems with sticking valves due to a lack of clearance betweenthe edge of the valve liner hole and the valve casing knuckle holes.We allknow this as the valves which stick after we have been playing for a shortwhile.It is easily fixed by gently scrapping the valve casing ports witha radius scraper(found in most tool supply catalogues) then lapping the valveswith a fine lapping compound (this is not the only cause of intermittantlysrticking valves).
Most piston valve sets utilize a spring box which mustbe properly aligned with the pump ports.The spring box(cylindrical tubingwhich holds the valve guide and spring) is most often times soft solderedinto the top of the pump tubing.During the assembly process, the slots guidingthe valve guide can be slighlty misaligned.If the spring box is not solderedat the proper angle, the holes in the valve will not align with theholes in the valve casing.To correct this problem the spring box must berepositioned so that the ports will line up correctly. To due this, thecorrect angle must be determined for the positioning of the spring box.Theholes in the valve casing and pumps will line up, side to side, if this isdone correctly.This is the first step in proper valve alingment.
The distance a valve travels is regulated bythe valve stem.In the resting position, the "Thru Ports" are aligned by theamount of material between the top of the spring box and the bottom of theupper valve cap. In the depressed position, the alignment of the valve slidetubing and pump ports is regulated by the length of the valve stem and theregulation material either under the valve button or on top of the uppervalve cap.Many times, a slight mistake in the machining of the valve casingcan cause severe mis-alignment problems with the valve ports. To correctthis problem, the proper distance must be determined between the ports aswell as the amount of travel. Small differences in the amount of travel cancause a horn to play stuffy or slightly out- of -tune. If the depressed travelis too short, the stem must be lengthened by placing a washer under the valvebutton or by refabricating the stem itself. If the depressed distance isto long, washers can be placed under the valve button.The resting positioncan be regulated by changing the height of the felts or cork uner the valvecap.
* It is impotant to note that on many horns if the regulation felts aretoo thin, the valve guide will click when the valve returns too its restingposition.This is caused by the top of the valve, at the connection betweenthe spring box and the valve, bumping into the guide on the upstroke.If thishappens, the spring box must be shortened to accomodate the extra regulationmaterial.
An accurate meaurement must be taken to determinethe distance between the "Thru Ports" and the top of the valve casing.Thiscan be accomplishd in a variety of ways.Several measuring tools exist toperform this function.By using small mirrors and gauges, a meaurement canbe established which will determine the proper distance to within a thousandsof an inch.
It is necessary to make sure that the top capsof any pistom horn screw down to the same position everytime they aretightened.Any slack can cause the valves to be misaligned as well as possiblycausing noise.
Although valve guides cannot be too restricted,they must not be allowed to "Float" too far from center.A loose guide willcause a valve to be misaligned from side to side.Valve guides can be builtup slightly to remove slop. Valves have a natural tendency to twist in theirrespective casings.This is directly related to the amount of pressure andair current flowing through the valve.Many times a valve will stick becauseof small imperfections along the slot which guides the valve guide. Afterfitting the valve guide, it is always a good idea to burnish the guide slotso that it is free of any restrictions.
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