Orifice Bleed Uniformity
By Phil Dayson
A couple of people have suggested to me that the small brass bleed cups that are sold by the Player Piano Co are not sufficiently uniform. I thought it might be interesting to take a random selection of bleeds, measure the leakage and look at the uniformity. The results of the test are tabulated below.
Flow, cubic inches per minute:
62 XXX
63 XXX
64 XXXXX
65 XXXXXXX
66 XX
Total bleeds measured: 20. All bleeds were #68 hole size (.0310-inch diam.) and were measured using 6 inches of water vacuum. For comparison, the flow through a #64 (.0360-inch) bleed cup (the next larger available size) was 97 cubic inches per minute. I don't have enough experience to know whether this is acceptably uniform or not.
There is a factor other than hole size which can have a substantial effect on the flow through a bleed. Quite simply, it is sharpness of the orifice-hole entrance. A sharp entrance will have a lower flow than a beveled or rounded entrance.
For example, one of the bleeds from the above test was selected: it had a flow rate of 64 cubic inches per minute. The entrance face was sanded flat so as to give a sharp entrance; the flow dropped to 61 cubic inches per minute. Using a small drill bit in my fingers the orifice entrance was given a very slight bevel: the flow increased to 73 cubic inches per minute.
I hope one or two restorers might find the above of interest.
Phil Dayson |
(Message sent Fri 28 Feb 1997, 06:48:46 GMT, from time zone GMT-0800.) |
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