LaserUser.com Forum (formerly RDWorksLab)

For those of you with an 80W China Red, check the cooling flow of your unit !

My China Red, with a relabeled EFR F2 tube, requires a MINIMUM cooling flow of 2 L/Min. I had the factory installed in line flow switch fail, and then shortly after, the tube itself failed. When the switch failed, I only noticed it because of the puny cooling water flow.

Russ identified my tube as an EFR F2. My minimum cooling flow is 2 L/Min. Spec is 2 to 5.

The nice big aquarium pump, as opposed to a real water pump, once restricted down to the 9mm tubing and 7 mm or less fittings, is putting out just over the 2 L/Min with no restrictions. Put their crappy in line flow switch in, and it's down to less than 1 L/Min courtesy of the restricted centrifugal aquarium pump. I would estimate my cooling flow during the time of switch malfunction to be in the .5 L/Min range. Only my short one or two project use kept the tube alive this long.

Fighting the manufacturer now, Hope I can save someone else the trouble.

Excellent warning. Let us know how you do with the manufacturer. If your machine is fairly new and still covered by some policy of your payment method (PayPal or credit card), get them involved ASAP. That often is the only way you get meaningful help from a seller.

Back when I had a real job I sold Industrial Pumps for a living including coolant pumps for machinery. Most and these like the Aquarium pumps used while they state volume X that is only at open flow (no pipe/hose) and only produce very slow pressures. Below is a rough guide that might help with why flow is or isn't X.

Typical Curve looks something like this.


This is only for reference and the numbers are not particularly important. It is fairly typical for the small aquarium pumps to have a maximum discharge head or pressure of 1.5-3m TOTAL, Looking at the sample curve by placing your reservoir container on the floor you already have to push the water up the approximately 1m into the Tube. LOSE 25% of the flow before you start pushing it through a hose.

Pipe Friction through small tubes is the next part so let assume a 3m tube run to the Laser and I have done some calculations rather than confuse to much. It isn't rocket science but the charts need a lot of explanation so I haven't shown one. Simple Online Calculator here if you want to have a bash https://goodcalculators.com/friction-loss-calculator/

Friction Loss For 3m of Plastic Tube.

0.5 LPM
6mm 0.088M
8mm 0.022M

1.0 LPM
6mm 0.318M
8mm 0.078M

2.0 LPM
6mm 1.147M
8mm 0.282M
10mm 0.095M

4.0 LPM
8mm 1.02M
10mm 0.344M
12mm 0.142M

So you add this number to your Static Head and then consider another FUDGE for the Tube losses and you can very quickly chew up the Aquarium pumps flow and pressure. The Return pipe is generally open and downhill so I would consider it about break even (could also be a slight reduction overall) and partially filled so a number would be rubbery.

Short Constrictions such as fittings or sharp bends do have an effect but unless they significantly reduce the flow area (>30%) I wouldn't worry to much. The numbers can be done per fitting or looked at like an orifice plate but keep them as few as possible avoid kinks in the hose.

What this means in a nutshell is no Laser should be using 6mm Tube EVER. Even my little 40W runs 8mm. For those of you with larger Lasers seriously consider stepping the hose up to 10mm for as much of the run as you can. Lastly consider moving your reservoir up vertically toward the Laser if you are still struggling with Flow as it is the largest part of the equation when you sort out the pipe friction. Worst case is go up a Pump Size but run bigger hose before that.

Luckily I got it through Amazon. I've already had to deal with a master power switch that wouldn't shut off, and an exhaust blower that if it stopped in just the right spot I had to pull the output tube, nudge the impeller a bit, and then put everything back together and away it would go. Took getting Amazon in the loop to get that resolved.

The bad part is that I had all the information in front of me, I just didn't double check what I had.

Russ figured out what tube I had from a picture and forwarded me the EFR page on it. The cooling flow wasn't the greatest, but it wasn't all that bad. I never thought to actually check the flow with a jug and stop watch and compare it to the spec. The pump that is labeled 2800 L / Hr through a 1/2" fitting will only put 2 L/Min through the laser tube and about 10' of 3/8" tubing.

I had to chuckle. I went back to look at the review I gave it before the flow switch / tube problem. Somebody else had a tube failure at less then 100 hours. Mine has less than 38... Gee, wonder if they had a cooling problem of some sort. I'm going to have to keep an eye out for a decent POND pump this spring at Lowe's / Home Depot / Menard's and upgrade my flow a bit. The cube refrigerator chiller is on the list of spring mods.

The switch and tube died just about the time the Spring Festival started up over there, and who knows what kind of problems they are having with that virus. I've sent emails almost every day, They are ahead of me by 14 hours, so my Sunday and Monday evening emails are their Monday and Tuesday morning emails. If I don't get a response in the next day or so I'll have to get Amazon back in the loop again.

With all the trouble I'm going to see if I can get them to upgrade me to the SPT TR90. The TR90 is so close to EFR F2 80W it's not funny. 1Ma power difference, and the TR has a 3V red laser built into the tube. So the 90W is AFTER the red laser, no 5% loss through the combiner lens and mirror !