ACHRNEWS

New Valve Takes a Step in the Right Direction

May 22, 2000
There’s a relatively new electronic valve on the market that controls evaporator pressure in order to keep refrigerated case temperatures where they should be.

Located either in the case or on the rack, the electric stepper regulator (ESR), also called an electric stepper valve, works with a controller and a temperature sensor to ensure accurate temperature control.

The ESR has the same basic function as a conventional mechanical regulator, in that it controls evaporator temperature by regulating the pressure in the evaporator coil. However, a mechanical regulator relies on the pressure-temperature relationship in order to achieve the proper temperature.

With an ESR, the correct temperature is input into the controller, and it controls to that temperature. There are no mechanical adjustments to worry about.

Easy to select, size, maintain, and install, the manufacturer (Alco Controls) says that the ESR can work well in many different refrigeration applications.

Selection And Use

While an ESR can be used in case control, the most obvious place to use it is on a rack. That’s because only a small percentage of cases (less than 10%) have electronics on them.

However, 60% to 70% of the racks today have electronics on them, so it makes more sense to use an ESR on a rack, where there are multiple cases that are controlled by one circuit.

With Alco Controls, there are only two sizes of ESRs, so it’s simple to choose the correct one. The company has capacity tables that show the different pressure drops that are required, so all a technician needs to do is figure out the worst-case scenario and make the selection based on that.

It is a very simple device, says Mike Noble, business unit leader, Alco Controls, St. Louis, MO.

“There’s a fundamental difference between the mechanical and the electrical products, and that is the mechanical products need a 2- to 4-lb pressure drop across the valve in order to make it work. It has to have that. So if you oversize the valve, you won’t get the required differential, and it won’t operate. If it’s undersized, then there’s too much restriction and you pay an energy penalty.”

Because the ESR is motor operated, it doesn’t make any difference if it’s oversized; the worst thing that will happen is that the customer is paying for more capacity than needed, but other than that, it will still function just fine. “We’ve tested stepper valves operating very close to the seat on very small applications, and they still maintain good control,” says Noble.

If There’s Trouble

It shouldn’t sound as if the ESR is absolutely no trouble to select and install. There is a learning curve that’s involved, because technicians must be knowledgeable in how the valve works, what kind of user inputs are required for the controller, and how to start up the system.

It’s not like a mechanical device; an electrically driven valve must have sensors and a controller. And all must function together for proper control.

If the valve isn’t working correctly, there are only two possibilities — either a bad valve or bad electronics (controller/sensors).

“The valve only does what the controller tells it to. So either the controller isn’t telling it to do anything, or the controller’s telling it to do something and the valve isn’t responding, which means you have a bad valve,” says Noble.

To find out whether the valve or the controller is the problem, Alco Controls came up with the “MTB1,” which stands for mechanic’s toolbox. It’s a simple device that the technician can use to determine the problem.

Basically, the technician can disconnect the valve from the controller, without having to break into the refrigerant system, in order to independently test the valve and the controller. If the valve responds to the MTB1, then it’s a good valve. Then the technician needs to look at the controller itself to see if there’s something wrong there.

If the valve is bad, Alco makes a repair kit, where you can screw the whole valve assembly out of the body, leaving the body in the line, so there’s no brazing required.

“The reliability on this product has been very good. Once it starts up and it works, there really should be no need to get back into this device at all.

“But again, if you do need to, then you can just unscrew it and then screw in a replacement,” says Noble.

Replacing Alco’s stepper valve with another manufacturer’s valve is not as simple as replacing conventional valves, however. Sporlan is the only other manufacturer that makes a direct stepper valve competitor, but the Sporlan ESR is different from the Alco ESR in that the step rate is different. So it’s not possible to take out an Alco ESR and replace it with a Sporlan ESR without making other changes to the software settings.

The stepper valve works so well, says Noble, that you should be prepared to see it in more applications in the future.

“We’re going to see a lot more products in the next few years — such as subcooling with stepper valves and heat reclaim stepper valves.”