Introducing a Gas Control System for Bulk Supply Systems
To introduce an efficient Control System into factories that already have a purpose built gas supply either in the form of a bulk liquid or palletised cylinders with a common manifold, is an area we have enjoyed developing a range a specific products. We must always remember the three elements which govern the accuracy, stability, volume and pressure of the delivered gas to the weld pool, these being;
1) The load mechanism provides the means by which the operator is able to set the force that determines the outlet pressure.
2) The sensing element senses the changes in the outlet pressure. This sensing element is also the link between the loading element and the control element.
3) The control element reduces the inlet pressure to a lower working pressure and maintains it by increasing or decreasing the inlet orifice size.
The interesting thing about adding to a system that is already in place is that, these elements have been addressed to some degree, so we need to assess the supply system and then create a strategy to improve the Gas Control to an even higher level of efficiency. This is generally not a complicated procedure. Any bulk supply will be supplying what we will call a ‘Ring Main’ (RM) with a regulated pressure, anywhere between 40 psi and 120 psi, this will depend on;
a) Type of supply. Bulk Liquid or Cylinder Packs.
b) Number of welding machines to feed
c) The floor area of factory it is feeding
d) The installer
The RM will then generally ring the area to be supplied with droppers coming down to supply each individual welding bay or machine or even a bank of machines. We have seen RM supplying only four machines but more commonly twenty and up. At the end of the droppers, will be an isolation valve and some form of control. Some would use a flowmeter and others a regulator.
So we need to establish;
1) Ring Main pressure. This can be often read off the regulator on the bulk system. If this is not possible then you can use the tester to check the line pressure.
2) The control type at the end of the dropper.
Once these points are established then we can create the strategy to give your client the advantages of a complete Gas Control System. So going back to our main points and what we have done with our Compipe series of gas controllers, to provide the strategy needed;
This is the first basic part of any regulator mechanism; it is the means that determines the desired outlet pressure. The load provides the force that is transmitted through the sensing device to the control facility, in turn giving the desired outlet pressure. The Compipe series uses a specifically loaded spring designed to load a control element sealing between 5psi and 200psi, and sense the movement of a 1 ¾” dia. Diaphragm.
We have opted to use a reinforced rubber product to manufacture the diaphragm for the Compipe series. The increased sensitivity of this product makes this a good option. The down side of using a rubber compound is its relative low strength when compared to Stainless Steel, but we have designed the Compipe series to shut down if the supply pressure exceeds 400 psi, which is well within the pressure rating of the diaphragm. This diaphragm will sense and react to pressure changes as low as 0.25 psi.
Control is achieved by the use of a valve which opens and closes, to give you more or less flow. This is the real secret of the Compipe series because by combining the valve design and the loading and sensing elements we have achieved what has proved to be difficult to do by traditional means that is to provide consistently low pressure, low turbulence, and consistent flow control. The Compipe series use a spherical valve seating on a pre-tensioned high density seat which is especially machined to provide point contact only. As the seat opens this is carefully monitored by the seat shape to expose flow area exponentially. This valve design provides smooth gas paths which reduce turbulence, especially noticeable in Aluminium or Galvanised welding situations. The seat has a very low coefficient of friction which enables it to reseat at less than 2% of flow pressure.
We have added another element to the factors behind successful Gas Control, and this is by no means something that should be taken lightly. INSTALLATION. It is very important that we understand what we are trying to achieve when it comes to controlling the gas shield to a weld pool.
We need an inert gas to protect the molten weld pool from contamination from the atmosphere. This shield needs to be adequate to do its job but not to the point that it can create other problems. The shield needs to be consistent in flow; if a flow is inconsistent operators tend to increase the flow to cover all situations. And we don’t want surges of pressure; either at the start of a weld or during a welding pass.
So we need to provide the shield gas at the correct flow at the lowest possible pressure. To achieve this you need to regulate at least twice and the last regulation point as close as possible to the gas solenoid as possible. The Compipe series comes complete with a mounting kit and either adjustable, Lockable or preset models, so you can mount just before the solenoid. Remember our Compipe series will give you 15CFH of gas at a regulated pressure of less than 3psi. If for safety reasons you cannot mount this close to the gas solenoid then the hose length should not exceed nine feet and the internal diameter of the hose should not exceed 7/32”. Any hose or pipe downstream from the last regulation point should be viewed as a storage reservoir which empty’s out every time you open the gas solenoid and then fills up again when you close it.
Correct gas control will result in;
1) Lower gas flows needed
2) Lower amperes needed
3) Less clean-up time
4) Faster response times
5) Longer lasting solenoids
6) And substantial Gas Savings
This dialogue is by no means meant to express the whole idea behind gas control but only to outline the basic principals that we need to understand to begin this pathway to total efficiency
The Design Team
PMC Gas Controls Aust. P/L