Question-Answer session that provides a birds-eye view of the Cricket Air Circuit.
What are the Basics of How the Air Circuit on a Utility Air Hammer Works?
The core design of an Air Circuit is actually a fairly simple concept.
A ram is connected to the rod on a double-acting cylinder. The cylinder has two external ports (front and rear) and an internal piston with the attached rod extending through the front of the cylinder. Pressurized air that enters the rear of the cylinder pushes on the piston and moves it toward the front of the cylinder… pushing the rod out the front of the cylinder, and moving the Ram away from the cylinder. Conversely, when pressurized air enters the front of the cylinder, it pushes the piston back toward the rear of the cylinder, retracting the rod into the cylinder and moving the Ram back toward the cylinder. This sequence is repeated over and over, cycling the ram, allowing the operator to forge objects.
While air is being pushed into one end of the cylinder, the air on the opposite side of the piston is being pushed (by the piston) out the other end of the cylinder. This air is routed out of the Air Circuit to a muffler.
What Controls the Air Movement through the Air Circuit?
This involves discussion of several separate actions. Each action, and its associated components will be discussed in the following paragraphs. A series of valves that are inter-connected (with fittings and hoses) interact with one another to control the flow and volume of air passing through the Air Circuit. Butterfly Valves are used on the front and rear ends of the Air Circuit. They will (hereafter) be referred to as “Butterfly Valve 1” and “Butterfly Valve 2” respectively.
A butterfly valve is similar in function to a common ball valve in operation. The difference is that the butterfly valve has a wafer inside (to allow air passage) instead of a ball.
A butterfly valve is used in lieu of a ball valve because the volume of air allowed through is more proportional to the handle movement than the ball valve is.
Pressurized air enters the front of the Air Circuit (Air Input Side) and exits the back end of the Air Circuit (Exhaust side).
Will the Ram start cycling when Butterfly Valve 1 is opened?
It shouldn’t…. and if the treadle is in its fully-up position (and everything is working properly), it will not. The Ram will however, rise to its highest resting position and remain stationary. Opening Butterfly Valve 1 “Charges” the air circuit with pressurized air. It does not initiate cycling. It only prepares the circuit to be able to quickly initiate cycling.
When does the cycling begin?
The Ram will begin to cycle when Butterfly Valve 2 is opened… when the operator presses down on the Treadle.
The lever on Butterfly Valve 2 is connected (via chain linkage) to the treadle. Butterfly Valve 2 is opened and closed by movement of the treadle.
Butterfly Valve 2 is used to control the volume of air passing through the Air Circuit. When Butterfly Valve 2 is closed, no air is passing through the air circuit.
Even though the butterfly valve on the front end of the system is open, it doesn’t mean air is continuously passing through the air circuit…. It only means air can enter the air circuit. Butterfly Valve 2 must be open for air to flow through.
If Butterfly Valve 2 is opened a little…. A little air (think volume) is allowed to flow through the air circuit. If Butterfly Valve 2 is opened a lot…. A massive volume of air can flow through the air circuit. The amount of air (in volume) allowed through the air circuit is (ideally) proportional to the amount Butterfly Valve 2 is opened.
So far, we have described components (butterfly valves) that control the entry, exit and volume of pressurized air that passes through the air circuit. It should also be understood that the “Primary Control” of air passing through the air circuit is at Butterfly Valve 2.
Think about the volume of pressurized air moving as being “metered” by Butterfly Valve 2.
You seem obsessed with volume…. Why is the volume of air passing through the air circuit important?
Earlier, it was disclosed that air enters the the rear of the cylinder to push the ram up…. and air enters the front of the cylinder to pull the ram back down. Air volume is significant because it takes a specific amount of air (in volume) to move the ram each way. Think of the amount of air (in volume) it takes to move the ram each way as a “Gulp” of air. If a single gulp of air passes through the air circuit every second, the ram could (potentially) cycle 30 times a minute (it takes 2 gulps to cycle). When the treadle is in its fully-up position, no pressurized air is moving through the air circuit. As the treadle is pressed down, Butterfly Valve 2 is opened further and further, allowing an increasing volume of air to flow through the air circuit. When the treadle is pressed just a bit, only a few gulps of air (per minute) will flow through, cycling the ram slowly. As the treadle is pressed down more, more gulps of air (per minute) flow through and the ram cycles faster. When Butterfly Valve 2 is fully opened, the ram will cycle in excess of 200 times a minute.
OK…. I understand that air enters and exits the air circuit, but discussing simple air flow doesn’t account for the Ram dynamically changing direction. What makes that happen?
This is where we discuss the “Heart” of the Air Circuit.
There is a Directional Flow Control Valve (hereafter referred to as the “4-Way Valve”) that manages the cylinder changing direction.
The 4-Way Valve has hose connections to the front and rear of the cylinder. As pressurized air rushes into the Air Circuit, it enters the 4-Way Valve and is routed to either the front or rear of the cylinder. Initially, when the operator has opened Butterfly Valve 1, the 4-Way Valve is conditioned to route incoming air to the rear of the cylinder. This is why the Ram rises to its upper-most position.
What do you mean when you say the 4-Way Valve is “Conditioned”?
The 4-Way Valve has an internal (movable) object, called a spool, which moves in a sleeve and configures the pathways through the 4-Way Valve. The spool has two positions. When its in its initial position, pressurized air coming into the valve is routed to the rear of the cylinder. When the spool is moved to its alternate position, incoming air is routed to the front of the cylinder. As the operator presses down the treadle, the spool moves to its alternate position. This action “re-routes” the air flowing through the 4-Way Valve to the front end of the cylinder, and causes the Ram to move down.
That only accounts for a single change in the direction the cylinder is moving.
How is cycling of the Ram accomplished?
As long as the treadle is pressed down, the spool moves back and forth, dynamically changing the path that air is flowing through the 4-Way Valve.
I assume something is controlling the spool… How does the spool know when to move to its alternate position?
Good question…. The spool is held in its initial position by a spring (pushing against one end). A second air valve, identified as the Roller Valve, is monitoring the position of the Ram. When the Roller Valve detects it’s time to change the direction the Ram is moving, it sends a signal to the 4-Way Valve to change the position of the spool.
How does the Roller Valve detect when it’s time to send the signal?
The Roller Valve has a lever on its side (with a roller on the end). The roller interacts with a ramp (part of the Ramp Dock Assembly). A signal is sent to the 4-Way Valve when the roller either moves up or down the ramp.
Is there a ramp for both the top and bottom of the stroke?
No, there is a single Ramp, which identifies the Nominal Center of the Stroke.
If there is only one Ramp, and a signal is sent to change the direction of the Ram when it is encountered, it seems like the stroke would be very short. What happens to allow the stroke to be long?
While it’s true that when the Roller Valve sends the signal, the internal pathways in the 4-Way Valve are immediately reconfigured (and air is rerouted to the opposite end of the cylinder), the Ram does not immediately reverse direction. It momentarily continues in the same direction (due to momentum) before it reverses direction. This action provides for half the cycle distance. The distance traversed is dependent upon how much air is trapped ahead of the piston in the cylinder and the pressure of the air entering to reverse the direction the Ram is moving.
The air ahead of the piston is trapped by the Check Valve and is further compressed as the Ram continues moving before it reverses direction.
This additional compression provides a direct performance boost for forging and planishing.
One more thing…. When the cylinder changes direction, air is being routed to the front or rear of the cylinder’s piston. As the cylinder’s internal piston is being moved, the air ahead of it has to go somewhere. Where does that air go?
It goes out the side of the cylinder and is used to blow up balloons…. If you believe that, I have some ocean side property in Arizona I want to sell you. The real story… The spool reconfigures pathways in the 4-Way Valve for exhausting air from the cylinder as well as loading the cylinder. As the 4-Way Valve is routing air into the cylinder, the air being pushed out by the piston is routed back through the 4-Way Valve toward a muffler. As strange as it may sound, this is where the magic occurs. It’s in this path of exhaust air flow Butterfly Valve 2 resides. The whole action of the Air Circuit is controlled by the volume of pressurized air allowed allowed to flow through Butterfly Valve 2.
This has been a brief description of the Air Circuit and its components. The Air Circuit diagrams and Component Details (Long Story) section explain the use of additional valves to support operations, superior performance and advanced features not mentioned in this overview.
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