A Simple and Easy-to-Make Reservoir Spill Valve

by Melvyn Wright

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A Simple and Easy-to-Make Spill Valve  (Relief Valve)

This is the way I make a spill valve to fit on the top of a reservoir.  Spill valves can be fitted on the inside or the outside of a reservoir, but I prefer to fit them on the outside for a number or reasons: They do not take up any room inside the reservoir so allow it to close completely; and they are completely accessible from the outside to allow for maintenance, cleaning and ajdustment, etc.

The size of this valve is suitable to fit a small organ like the John Smith Busker or Universal, but it can be made any size.  It will also fit my double-acting bellows.  In theory the valve should be at least equal to the size of the output port in the reservoir. This means that when the output from the reservoir gets completely blocked (as it does when no notes are playing) the valve will be able to pass the same amount of air.

Materials

I prefer to make my valves entirely from MDF, but you can use plywood or natural wood if it's smooth and flat enough.  You will need some scraps of MDF; a piece of leather approx. 48 x 30mm; and some piano wire (0.8 to 1.1mm) for the springs.

Method

Start with a small rectangular block of 9mm thick MDF, cut to 78 x 36mm.  This will form the Valve Base, and must be sanded absolutely flat.  Cut a rectangular hole in this, about 35mm x 16mm, using a fretsaw or scroll saw. This size of hole is roughly equivalent to a 1" diameter hose.

The Valve is made from a piece of 6mm MDF, cut to 63 x 32mm.  The piece of leather is glued onto the centre of this to form the Valve seal.  Sand the shiney side of the leather to roughen it up before applying the glue.  When fitted, the leather should overlap the hole in the Base by approximately 7mm all round.

I do not use a leather hinge for the Valve, as this method has proved to be quite unsatisfactory.  Instead of hingeing the Valve, I just  use two guide pins to hold it in place.  This method also has the great advantage of allowing the Valve to be completely removed and replaced in a few seconds, for instance when covering the reservoir.  Ordinary 1" (or longer) panel pins make suitable guide pins.  The heads should be cut off to make the pins around 24mm long.

Saw two guide slots in the Valve, as shown, on either side of the leather.  These are in the centre and must be wide enough for the pins to move freely along the slots.  Then place the Valve in position on the Valve Base so that the leather covers the hole, and knock the two pins into the Base so that the Valve can move freely up and down, guided by the pins.  Instead of hammering the pins straight in, I prefer to mark the positions of the holes at this stage, and then drill two pilot holes to take the guide pins.  This makes sure that they are positioned straight and vertical.  After installing the guide pins, drop the Valve into position and check that it can move freely up and down, and cannot move out of position.

Cut out the Operating Lever from 6mm MDF and glue it to the top of the Valve.  The joint can be strengthened by two small blocks of 3mm MDF either side.  Pushng down on the Lever will raise the Valve and uncover the hole.  Check that the Lever doesn't foul the pins when operated.  If it does, just cut away the offending area.  The Valve should be able to lift by about 20 degrees.

Now make the springs.  Take two lengths of piano wire and bend them around an 8mm rod (or drill bit) to form the springs.  I bent them just over 1 1/4 turns (see the top photo) but you will need to adjust this depending on the wire used and the size of the Valve, wind pressure, etc.  These springs are held in the Spring Block, which is a piece of MDF or wood 10mm square with two small holes drilled in it.  I prefer to use solid wood for this block, as MDF has a tendency to split under the pressure from the springs.  This Spring Block is glued onto the top of the Valve Base, as shown in the photos.  The springs are just held in place by friction.  Bend the spring tails as shown, so that they ride smoothly on top of the Valve.

Two thin strips of MDF are used to form spring retainers, which prevent the springs from sliding off the sides of the Valve.  It is much easier to do it like this rather than trying to cut grooves directly in the top of the Valve.  Any grooves would have to be quite wide and smooth to prevent the springs from jamming, certainly wider than a saw cut.

When finished, the Valve can be glued into position over the hole in the reservoir.  The Lever can either be operated by coming into contact with a fixed stop in the organ, or by a length of cord tied to the bottom reservoir board.  Check that the Valve seals properly and operates correctly.  As mentioned before, the springs might need adjusting to cope with the pressure in the reservoir if there are any leaks.  Ideally, the springs should be just strong eough to prevent leaks, and no stronger.  If they are much too strong it might affect the pressure in the reservoir when the Valve opens.
 

 
The main components of the Spill Valve
 


The leather glued to the underside of the Valve, and the slots made for the guide pins


The Valve Base with the 2 guide pins fitted. The Valve simply drops over these two pins


The Spring Holder Block added to the base
   


The Operating Lever is glued to the top of the Valve. Note the blocks glued on either side to strengthen the joint

 The Valve dropped into place over the pins, and the spring retainers added to form grooves for the springs to ride along


Fit the two springs.  Note that the Valve should be hinged at the end with the springs


Underside of completed Valve
 

Valve in open position

Notes

You might have noticed that the Valve Base is not really necessary.  It is quite possible to install the guide pins directly in the top of the reservoir, either side of the hole, and glue the Spring Block alongside.  I used to do it this way but have since come to realise the advantages of making the Valve assembly as a separate unit and glueing it on when finished.  This avoids any mistakes from ruining the reservoir, and also strenghens the guide pin fixing.

The Valve can easily be removed by rotating the springs away, and just lifting it off the pins.  This should be done now, in order to brush the leather with a toothbrush, and to trim the length of the Operating Lever as necessary.  Drill a hole in the end of the Lever if it is to be operated by a length of cord.

 

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