Testo 557 vacuum gauge and Appion core removal tools shown
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I've had a change of heart.
Back in the early s, during the big construction boom, I did many system startups on residential units for a large company I worked for.
When installers ran the line sets prior to startup, they weren't always very careful to keep them clean and dry. Many times, we would end up with a restriction in the piston or TXV.
These new residential systems come with a precharged refrigerant in the condenser. So, after my vacuum was complete, I would “release” the charge by slowly opening the liquid line service and watching to see if my suction pressure would steadily rise.
If there were anything in the liquid line, it would hit the screen or drier before the metering device instead of possibly running the other way and clogging the TXV or orifice.
I often knew that there was a restriction before I even started the system because I got used to watching that suction needle rise. While I did this for a good reason, that reason is in the past.
When we install systems, we take great care to make sure the line set stays clean and dry, and we flow nitrogen while brazing with the line drier installed near the indoor coil.
It's a new day, and I'm giving up my old sins.
So, now I must admit that the better way to do it is to open the SUCTION valve first (slowly!). That prevents oil loss out of the compressor into the discharge line and out of the liquid line.
It's unlikely that you will lose enough compressor oil to cause any damage by opening the liquid line slowly, but any oil that the compressor loses has a long journey before it gets back to the compressor. The other issue is that oil loss in those first few moments in the life of a new system can have long-lasting effects on the operation and longevity of that compressor.
Have you ever taken a liquid line hose off after a new system install and gotten oil all over?
That is often due to opening the liquid line first and the compressor losing oil to the discharge line and then to the liquid line.
When you open the suction side slowly first, oil loss from the compressor will enter the suction line. Once the compressor begins running, it will pull that oil back into the compressor.
When doing it this way, you would attach your micron gauge to the liquid line core remover side port with the Schrader in place in the side port. Once you completed your vacuum and proved you had no leaks or moisture by valving off the VCT's and watching your decay rate, you would then attach your gauge manifold and slowly crack the suction side until you see a few psi on the liquid side. Now, remove the vacuum gauge to ensure the system pressure does not damage it.
Most micron gauges can handle some pressure. For example, the Testo 552 can handle up to 72 PSIG (4.96 bar), and many can handle 400 psi (27.57 bar) or more. It never hurts to remove that expensive and sensitive micron gauge before exposing the sensor to high pressure. Still, it's never a good idea to remove it BEFORE the system is under positive pressure. If you do that, you will lose the entire vacuum.
You would then purge your manifold hoses and fully open the suction valve and then the liquid line valve.
When charging a system with no charge (not running), weigh refrigerant into the liquid line first until both sides equalize in pressure. That way, you can ensure that you are not introducing liquid refrigerant right into the compressor crankcase.
Also, keep in mind that it is good practice to run the crankcase heater once the charge has been released and before the system is started to prevent a flooded start on the compressor.
—Bryan
Published: August 1,
Last updated: December 30,
Knowing what makes a valve the right choice
Valves control gas and liquid flow in almost every process and system. As common as they are, choosing the right valve can sometimes be time consuming and confusing.
Begin valve selection by first gathering some basic information on system performance requirements. Knowing this will make it easier to find the right valve. The five tips in this article focus on how to match valve features with these requirements.
For more information, please visit Valve Opening Key.
Tip 1 – Valve size and type
Choose the right valve type. Every valve needs to perform one or more basic functions:
Function determines the design of standard valve types. These are some of the most common valve types:
Properly sizing the valve is also important. The right valve choice means matching the valve’s size to expected flow through the system.
Common Valve Types at VMA, Valve Manufacturers Association of America
How to Select the Right Valve (with Pros and Cons) at Indelac Controls
Tip 2 – Materials of construction
Know the chemical compatibility requirements. The valve materials need to be compatible with the gases or liquids flowing through it. Plastic valves usually resist harsh or corrosive chemicals better than metal valves.
Miniature Ball Valves: Plastic, Brass or Stainless Steel? at ISM, Industrial Specialties Mfg.
Chemical Compatibility Chart at ISM, Industrial Specialties Mfg.
Tip 3 – Performance requirements
Determine the pressure and temperature requirements. Find out both the temperature and pressure ranges where the valve will be installed. Metal valves tend to withstand higher temperatures and pressures than plastic valves. Metal valves are also usually best for pressurized gases. This is because they tend to be stronger than plastic valves.
A Selection Criterion for Pump and Valve Reliability at Processing Magazine
Tip 4 – Check valves have special requirements
Be sure the new check valve will work as expected. Look at the response time needed as well as the cracking pressure required to open the valve.
Another consideration is normally closed vs normally open. There are basic check valve designs that require positive downstream pressure to open. These are usually referred to as normally closed check valves. There are other designs that require a positive backpressure to close. These are usually called normally open check valves. An appropriate choice between these two can improve check valve reliability. It is usually best to base this decision on whether the valve is usually open more or usually closed more during normal system operation.
Some check valve types may not work properly if mounted vertically instead of horizontally. Flow direction (upwards vs downwards) and fluid density both matter for check valve designs that can be mounted vertically.
Checking Out Check Valves – An Introduction at ISM, Industrial Specialties Mfg.
Tip 5 –Maintenance
Don't forget to consider ongoing maintenance. Any valve choice should include attention to maintenance requirements. This is important for both valve reliability and application stability.
A good example of this are ball valves. They resist clogging, jamming or malfunctioning. But they are not suitable for adjusting flow. Using them to control flow can lead to leaking or premature failure.
Valve connection type affects the ease and speed of repair or replacement. Each connection type (threaded, barbed, push-in, Luer, and so on) has its pros and cons.
Plant and Equipment Maintenance at HSE, Health and Safety Executive
Knowing where to start makes valve choice faster and easier
There it is. Knowing particular information beforehand, makes choosing the right valve easier and more certain. There will always be complications like application requirements, operating conditions and chemical compatibility. Starting with basic valve requirements will simplify and speed up valve selection:
Some additional resources
How ISM can help you find the right miniature valve for your application
Personalized customer service and resources available at the ISM website can be a great help when selecting a valve. Available online resources include chemical compatibility reference guides, dimensional drawings and product data sheets. Our online and PDF flow control valve catalogs provide access to a wide variety of miniature valve types, connection types, materials and sizes:
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