Month: February 2017

In this episode Bryan speaks with Jim Bergmann about his path to being a test instruments business owner. we talk about –

– The Challenges in the past with poor quality instruments

– Enthalpy calculations

– The Future of test instruments and readings

– Taking readings with a pitot tube

As always if you have an iPhone subscribe HERE and if you have an Android phone subscribe HERE

In this video we cover the basics of using the Testo 510i with a pitot tube to do a duct traverse and easily calculate Velocity in FPM and volume in CFM on a small 8″ duct. Using this method is handy because you can use the reliable, accurate and inexpensive 510i to perform the measurement without any other equipment other than tubes and a pitot tube.

As stated in the video, a pitot tube is best (most accurately) used in the following conditions –

  • Medium to High Air Velocities
  • With 4 -8 feet of hose
  • In low turbulence air at least 8.5 diameters downstream of any turns, fittings or diffusers (I was less than this in the video resulting in lower accuracy)
  • In a duct at least 30 times larger than the pitot tube diameter (It was less than this in the video resulting in lower accuracy)

 

For more information see the following links –

Dwyer Guidelines

TruTech Tools Traverse Quick Chart

TruTech Measuring with a pitot tube

Testo 510i specs

Video on the performance of a rectangular time average traverse

Some quick basics –

An Ohmmeter is used to measure the resistance to electrical flow between two points. The Ohmmeter is most commonly used to check continuity. Continuity is not a “measurement” as much as it is a yes / no statement. To say there is continuity is to say that there is a good electrical path between two points. To say there is no continuity means there is not a good electrical path.

In other words, continuity means low or zero ohms and no continuity means very high or infinite ohms. Don’t get the terms zero ohms and infinite ohms confused, they mean opposite things.

 

This type of testing is commonly used to check fuses, Trace wires, check for short and open circuits Etc… Resistance readings are necessary for identifying motor terminals, and checking for a breakdown in insulation. An Ohmmeter continuity can be used to identify normally open, and closed terminals on a relay. Simply place the leads of the meter across the relay points, if there is continuity the relay is normally closed. Now apply power to the magnetic coil of the relay, the contacts that were closed should now open, or vice versa. An Ohmmeter can be used to identify a single wire in a bundle. Go to the opposite end of the wire and expose two separate wires in one sheath. Twist the two wires together and list the colors. Go back to the other end and check for continuity between all wires of that color.

 

Once you find two wires with continuity, you have found the correct wire. If you suspect that a particular wire is shorted to another wire, simply disconnect both wires on each end and check for continuity between the two wires. If continuity is read between the wires you have found a short.

These are only a few examples of ways to utilize an Ohmmeter.  Remember an Ohmmeter should only be used in un-energized circuits, Otherwise the meter could be damaged.

 

— Bryan

I’ve got a confession to make.
I’m ‘that guy’ call it OCD, call it being anal retentive, but I’m always making an effort to be as technically correct as possible, and one aspect of that effort has been the use of torque indicating or torque limiting tools when tightening fasteners.

 

It started after I put new valve plates and gaskets on a Carlyle 06E compressor. As I was always taught, all the torque you needed to apply to a fastener was the torque you could apply with a normal sized combination wrench, so that is exactly what I did. The compressor gaskets failed and were bypassing the very next day because I didn’t get those bolts tight enough. The tech who took that call asked me if I had and used a torque wrench. At first, I didn’t understand.. sure, I tighten the bolts. No, he asked, did you TORQUE them to specifications? 90-100 ft/lbs was the spec and, while you can get that kind of torque out of a standard length ¾”
wrench, you’re working at it.

 

That question started a dive down something of a ‘rabbit hole’ for me and I’m going to share
some of what I learned.

 

I started with one torque wrench, just to tighten the bolts on compressor heads. From there, I’ve expanded to have three torque wrenches (¼ ⅜ and ½ drive) and a torque limiting screwdriver mostly for electrical connections.

 

What is torque? Simply put, torque is a measurement of the amount of force required to turn a fastener. For bolts, torque is normally measured in ft/lbs or in/lbs. To help you understand a foot-pounds (ft/lb) or inch-pounds (in/lb). A foot pound is one pound of force applied on a lever one foot long measured from the center of the fastener.

 

As we continue to increase the torque applied to a bolt, the male threads on the bolt move deeper into the female threaded hole while the part being fastened, for example, a compressor head, prevents the head of the fastener from following them. This stress results in a stretching of the bolt. That stretch applies what is called ‘clamping force’ to the assembly. This stretching permanently deforms and weakens the bolts, and sometimes proper assembly requires
the use of new bolts. Lubricant applied to the fastener makes it easier to turn which decreases the torque required to achieve the same clamping force. Be careful to always follow manufacturer guidelines.

 
One place where torque wrenches are making inroads in our industry are with ductless mini splits. While I haven’t broken down and added one of these to my kit yet, I do have an easy way to torque flare fasteners using a regular torque wrench. Crowsfoot wrenches.

 

These little guys allow you to turn any ratchet or breaker bar into a handy wrench. To use them with a torque wrench, however, requires a little extra step.
Remember how we measure torque? It’s based on the distance between the center of the fastener to the point where force is applied. Well, a torque wrench is calibrated to have force applied on the knurled part of the wrench handle and centers that force on the centerline of the drive spindle. Adding a crowsfoot wrench to the end of the wrench changes the center of the applied force. What we need to do is account for the extra length of the crowsfoot and the extra leverage that
reates.

 

For this, use your required torque force as TA to solve the math. That said, I’ve found very little actual difference when using a crowsfoot wrench, and since often torque values are given in a range, it isn’t really necessary to calculate the difference, just set your wrench to the low end of
the torque range and use the crowsfoot. That will generally keep you within the specified torque range.

 

Another trick, where possible, is to install the crowsfoot at a 90° angle to the drive. Doing this makes the actual and effective length of the tool the same and allows direct use of the tool without calculations. Keep in mind that a standard socket drive extension won’t affect your torque wrench settings because it doesn’t affect the length of the tool in the direction that matters.

 

I hear a lot of guys argue against using a torque wrench because they can tighten things up just fine without one. Probably so. I did a lot of jobs prior to the one I mentioned earlier without using one and I was “just fine” or was I? Did I tighten those flanges evenly or did I warp the flange by over-torquing one side? Did I over-torque that flare and set myself up for a leak later? Did I tighten all the bolts evenly ensuring even clamping force on all those gaskets? A torque tool simplifies things for us. Tighten to specified torque, and you’re done. You don’t have to think about that variable anymore. It’s as tight as it’s supposed to be and no tighter.
It’s one less thing to worry about.

— Jeremy Smith

Diagram above by Carrier 

It’s really easy to put a liquid line drier in the proper location, it’s still more common that it gets installed in the WRONG location , namely, right at the condensing unit (OK it isn’t that big of a deal but for dramatic emphasis). Installing at the indoor coil is good practice for two main reasons.

#1 – It better protects the metering device (expansion valve or piston) from anything that may be in the liquid between the outside and the inside

No matter what, when you first put a unit in Service, you are either releasing the charge on the liquid line first or adding pressure in the liquid line. This means if anything is in the liquid line it is going to hit the indoor metering device first and putting the drier inside better protects the valve.

#2 – It won’t turn into a rusty mess and start leaking after a few years

This is pretty simple, so to make this tech tip a bit more in depth here are some other drier best practices.

  • Don’t “sweat” out an old drier. When you heat an old drier the moisture it has previously absorbed is driven out of the drier and back into the system. Cut it out instead.
  • Use the right type and size. Different driers have different purposes and vary in capacity. If you have a heat pump make sure to use a “bi-flow” drier. If you are mitigating a burnout ensure you are using a burnout suction drier. Make sure the capacity of the direr matches the capacity of the system, this will take a bit of reading. However for residential systems you can use 8 cu/in on small tonnage systems only. To be safe I would generally stick with 16 cu/in liquid line driers (chart by Parker / Sporlan)

  • Don’t burn the paint on a drier when installing. Not only will it look ugly, it will be more prone to corrosion. Use a damp cloth or other heat control methods.
  • Point the arrow in the correct direction. Suction driers point towards the compressor and away from the evaporator. Liquid line driers point toward the metering device and away from the condenser.
  • A liquid line drier goe in the liquid line NOT in the discharge line. The discharge line is between the compressor and the condenser. The liquid line is between the condenser and the metering device.
  • Flow nitrogen while brazing and pull a proper vacuum. Both of these practices are more important than whether a drier is inside or outside.
  • Remove all old line driers and install a new line drier whenever the system has been open and exposed to the atmosphere. Sometimes the old ones were in the wrong place, if so, go ahead and straight pipe them and install your new filter / drier in the proper location.

— Bryan

 

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