Sandwich Flow Controls

Sandwich flow controls are designed to be used with either sub-based or manifold-based compressed air valves. If you are not familiar with them, they can make adding flow controls to a circuit pretty easy. Here's information to help you better understand this air valve technology.

In a hypothetical example, we have just installed ten sub-based, individually mounted, air valves. The bases are connected together to make a bank of ten valves.

Or, we might have a single extruded manifold base on which we have mounted the same ten valves. Each of those ten valves is controlling a double acting air cylinder. This link takes you to a page of information on this site about this type of air cylinder.

On our hypothetical machine we need to be able to control the speed of each of the actuators on it. However, no two are to be operated at the same speed. Therefore, in order to be able to independently control the speed of each air cylinder, we will need to install flow controls for each of the cylinders.

What will be easier, installing 20 individual flow controls, one for each cylinder air line, and forty fittings if the flow control is in-line and does not come with instant fittings attached, or to install ten sandwich flow controls, one for each compressed air valve?

Sandwich flow controls - MAC valve
Older MAC Valve sandwich flow control

Sandwich Flow Controls

You will, of course, have made sure that when you selected the compressed air valves that they were built to use sandwich flow controls, right? That being the case, the sandwich flow controls are the obvious choice.

Installing Sandwich Flow Controls

Simply remove each valve from the sub-base or the manifold - usually by removing two or three bolts running through the valve from the top and into the base.Place one sandwich flow control on the base or manifold in the same location from which you removed the valve body.

Ensure that the gasket that came with the sandwich flow control is carefully positioned between the flow control and the base.

Replace the valve on top of the sandwich flow control. The same gasket that originally sealed the valve to the base, will now seal the same valve to the flow control.

The flow control will normally include bolts long enough to travel from the top of the valve, through itself, and into the base. Do not throw out the original shorter bolts, as you may need them should you wish to remove the flow control in future.

Unidirectional Flow Controls

The sandwich flow controls are meant to be installed on the base or manifold in one orientation. When all ten of these flow controls are installed all will present their adjusting screws on the same end for operator convenience in speed adjustment.

One of the problems with in-line flow controls is that they can be installed backwards, which prevents them from functioning normally. The typical sandwich flow control cannot be installed incorrectly.

The sandwich flow control mimics the action of the valve exhaust flow controls by controlling the outflow of the cylinder air at the air valve.

Do note that each brand of sandwich flow control is propriety, meaning that one manufacturer's model will likely fit no other base.

Too Long Air Lines?

A too long air line has the potential for a problem with controlling the cylinder speed.

If the air line from the cylinder back to the valve bank is long enough, the cylinder may have already traveled its full stroke before the back pressure created by the sandwich flow control can slow the flow of exhaust air and in doing so the speed of the cylinder.

If that is the case consider using in-line flow controls installed nearer to the cylinder, or the installation of in-port flow controls right in the cylinder ports. This will provide almost instant air cylinder speed control albeit with a lot more plumbing inquired than if the sandwich flow controls were able to be used.