snagboat accumulator

[aostling]

I've just returned to Phoenix after a 4,515 mile trip to Seattle, north up the coast, back through Yellowstone and the Rockies.

In Anacortes, Washington, I toured the snagboat W. T. Preston with my cousin and her husband, who live nearby. I remember seeing this steam-powered stern-wheeler when it was in operation. It's never-ending task was to locate and remove deadheads (partially submerged logs) from all the waters of Puget Sound.




The snagboat draws only three feet, so the engine room occupies the main deck. Here is a sketch of the equipment:






I don't recall what this pear-shaped apparatus was attached to. I think it is called an accumulator, but I'm confessing my ignorance. I'd like to hear from somebody who can describe its function.

[BigBoy1]

I would say it is a device to act as a "buffer" to prevent the water hammer effect. The water hammer effect is the banging that is heard when a water valve is closed extremely fast. The energy of the moving water has no place to disipate so it slams into the piping, casuing the loud banging. If the length of the pipe, water flow and velocities are great enough, the pipes can be ruptured by the water hammer effect. The electrically controlled solenoids on cloths and dish washing machine are the source of much of the water hammer banging in the home.

The accumulator is mounted close to the valve in the line where the flowing water will passing. The pear is 1/4 to 1/2 filled with air and the air cannot escape as there is water in the lower part of the pear. When the water valve is rapidley closed, the moving water compresses the air and disipate the energy of the moving water, eliminating the hammer effect. It cannot be seen what type of equipment "the pear" is mount upon but with the pipes and gage, I would think it has something to to with water/steam.

[wierdscience]

IIRC a Barametric condenser,it provides a vaccum impulse between stages in a multi-stage steam injector.

Here is a long read on early steam technology,with a breif section on injectors.

http://images.google.com/imgres?imgu...a%3DG%26um%3D1

[Evan]

I'm more interested in the "steam ram steering engine". I presume this is equivalent to a hydraulic ram but uses steam instead, a form of power steering. This brings up the question of how the pressure is maintained at a particular value to prevent the ram from changing position as the steam condenses. How is the condensed steam dealt with as the ram fills with water? How is the steam admitted to produce controllable movement?

[aostling]

I'm more interested in the "steam ram steering engine".

Here's a photo of the steering engine.

[JCHannum]

From the photo, the "accumulator" appears to be on the head of a steam pump, possibly feed water or for the water jet. It is an expansion chamber, the same as on many pumping systems to smooth the flow.

The steering engine appears to be a steam cylinder that moves the rudder. The rudder position is set by the screw mechanism which operates the cylinder valve. The vertical chain at the rear is from the helm to set position. If the rudder moves, steam is let into one side or the other of the cylinder to maintain the position. It is probably a bit more involved than that, but that is the basic operation.

Pressure is maintained in the cylinder by removing the condensate with some form of steam trap. The steam supply is to the valve chest at the top of the cylinder, the line to the left is condensate return.

Thanks for the photos and drawing, the main deck would be a live steam modeler's dream to build.

[jimmstruk]

How about the 2-71 engine with open exhaust?? JIM

[Willy]

Actually I noticed that too, I thought it was a 2-53 Detroit Diesel.

According to this we are both wrong as they list it as a 3-71.

More photos here.

[Bguns]

I was onboard it in Everett. They had the Spuds down, and main engine set at ahead dead slow...

Watching the connecting rods and cross slides run several feet back and forth was interesting.

At both ends of the stroke, was a small pool of oil that a leather strap dipped in, and spread along the ways...

[aostling]

I was onboard it in Everett. They had the Spuds down, and main engine set at ahead dead slow...

That must have been fascinating, to see the snagboat in actual operation. Those spud anchors where 20-odd feet long. The spuds plunged into the soft mud of the river bottoms, holding the boat against the swift current.

Here is a photo of the foundry pattern for the spud points: