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Old 10-11-2011, 10:57 AM
 
Join Date: Apr 2006
Location: Paducah, KY
Posts: 289
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In regard to the whistle on the American Queen not being loud enough, the problem is not with the whistle itself, but with the inadequate size line supplying it with steam from the boiler. The cross sectional area of the supply line to a whistle should never be smaller than the area of the slit admitting the air or steam. In actuality, the area from the supply line to the whistle's inlet should be twice the area of the annular slit. This is a mistake often made (and paid for by poor performance).

Many calliope whistles use bowls so thin that the area between the inlet to the back of the languid plate chokes the flow. This was the problem with the original 3 bell Davis chime on the Mississippi Queen. The whistle would have been awesome, had it been given deeper bowls that did not choke the flow from the inlet. When the whistle on the Delta Queen was moved from its old position near the stack to its current position, they also reduced the size of the supply line and compromised the whistle's performance. They afterwards ended up adding a piston horn as an additional sound signal. Everyone knows that a WHISTLE is the traditional voice of a steamboat.

Have you ever considered just how much power it takes to blow a whistle? It's a lot more than most people would think. Since most people blow whistles from a boiler or a compressed air tank, the volume of reserve steam in a boiler or compressed air tank can make a relatively small source appear more powerful than it is, at least for a short time. It's similar to trying to run a circuit with a high peak current demand from a small power supply with a large filter capacitor across its output. It may be able to supply brief peak demands but will ultimately fail in supplying the required power to the circuit. What we're talking about here is the power required to blow a whistle continuously to its full output. The analogy between the electrical power supplied to circuit and the mechanical power supplied to a whistle is the same. They can both be measured in Watts. The key word here is "continuous" power. A small supply line to a whistle is also analogous to trying to use a common lamp cord as a booster cable to charge a car battery.

Some whistle catalogs (Lunkenheimer and Kahlenberg) will give you consumption ratings at a given pressure in CFS (cubic feet/second). To convert this to CFM multiply CFS by 60. You'll then find out that as a rule of thumb a whistle of 3:1 scale will require around 100 CFM/inch in diameter to fully blow at a cutup of unity. Raising the cutup above unity will increase the required blowing pressure and CFM well above this. A whistle of larger 2:1 scale will require even more consumption of approx. 140 CFM/inch in diameter. A high flow rate at a high pressure means lots of horsepower will be required to continuously blow a large whistle. A whistle the size and scale of the 10" Lunkenheimer on the American Queen can use upwards of 1,000 boiler HP!

Thankfully we now have ways to minimize the required flow rate and pressure that a whistle requires to fully operate, while still obtaining a high acoustical output from it by modifying its design. With a simple change in the slit width, a whistle's efficiency can be increased by 500% (5 times)! A different bell design can further increase efficiency by 400% (4 times), giving a total input power reduction of 20:1, all without reducing the output! We have discussed the means of how to go about doing this on many occasions on the Yahoo group, Steam Whistles, of which several here are also members.

In a nutshell, whistles do need high flow rates as compared to air horns, but they do not need the traditional high pressures to perform well. The loudest whistle on record required a mere 15 PSI and used 1800 SCFM to produce an SPL of 85 dB at 1 mile, supplied by a 150 HP Roots blower. Google U.S. patent 4429656. By inverting and horn loading my former design I have a design that only requires 15 PSI at 1350 SCFM, yet produces 135 dB at 100 feet, a full 10 dB louder on axis than my former patent, supplied by a 100 HP rotary screw compressor. Google U.S. patent 4686928. It would take three 50 HP sirens to equal it's area of coverage.
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