Blast gate placement

[jussi]

Does it matter if it's closer to the tool or the DC?

[Tom Miller]

Many suggest to keep blast gates as close to the DC as possible. But I think if you don't have very leaky lines, and you have other constraints/desires, don't worry about it.

Regards,
Tom

[dbhost]

If you want to keep your CFM up, I would suspect you would want your blast gates as close to the tool as possible, with as short of a segment of flex hose as possible.

Having said that, it might not hurt to have a blast gate in line somewhere to shut whole segments of the plumbing network off...

Make doubly sure that your ducting does NOT leak and the longer distance from the DC becomes an advantage...

[jussi]

1 for closer to the tool 1 for closer to DC. Anyone care to break the tie

I just started using the DC (even though I bought it some time ago) and am only using the standard Y connector and 6' (or so) hose it came with. I don't think there are any leaks but is there any way to check? I just got a 10' flex hose from Rockler with a quick disconnect. Right now I only plan on using 2 hoses and 2 blast gates and using the quick disconnect. Probably just leave the shorter hose on the TS and move the longer one around.

[LarryG]

Break the tie? Well, here's a quote lifted directly from Bill Pentz's web site. The emphasis in the third sentence is his, not mine:

"You close the airflow to a machine with a blast gate. There are many different types of blast gates including many that can be opened automatically through electric motors, air pressure, and even hydraulics. The best place to put your blast gates is next to the wyes off your main line up high. The more open pipe or hose you leave exposed between the main run and the blast gate, the more resistance it causes."

Right or wrong, that's the way I laid out my system. I put all the blast gates immediately following the wyes off the main branch; where appropriate, I extended the hard pipe on the "upstream" side of the gates to get as close to the machine as I could before switching to a short piece of hose for the final connection. That's to say, many systems locate the blast gate at the point of transition from pipe to hose, as Dave seems to be saying, but you don't have to put it there.

[Rich P]

Since everything in my shop is mobile, I put the two aluminum gates at each leg of the wye going into the HFDC. Most times I'm only running one tool so I leave the other gate closed and just swing the hose to another tool as required. One of these days I'll get a real shop and will have to worry about such things.

[dbhost]

That would make perfect sense... I read the Pentz site bit you quote, I only caught the part about making sure you didn't expose any more hose than has to be...

[Tom Miller]

...a quote lifted directly from Bill Pentz's web site...."....The more open pipe or hose you leave exposed between the main run and the blast gate, the more resistance it causes."

Yeah, that's the argument that I was implicitly referring to. While being a fine guiding principle, I don't think it's that big a performance factor (again, assuming your lines aren't too leaky). So, the point I was making in my wishy-washy "non-vote" was: don't make your gates hard to get to, etc., just because of it.

Re: checking for leaks. If you can't hear it, it's probably fine. In other words, don't kill yourself looking for little 1-2 cfm leaks. The place where you do want to check for small leaks is on the pressurized side of your system (i.e from the impeller to the bags, including the bag seals). A small leak here can pump a lot of fine dust into your air. Sometimes, you can see telltale dust at the leak.

Regards,
Tom

[LarryG]

While being a fine guiding principle, I don't think it's that big a performance factor (again, assuming your lines aren't too leaky). So, the point I was making in my wishy-washy "non-vote" was: don't make your gates hard to get to, etc., just because of it.

Yes, I understood that, and I agree. In a shop with 10' ceilings and the main trunk that high, you wouldn't want to have to climb a ladder every time you needed to open or close a gate. At some point performance and convenience have to merge.

We need a mechnical engineer like masteryoda to weigh in on this one. I want to say that I saw more sources than just Pentz say to put the gates near the main trunk. Of course, with Pentz's site being a well-known and oft-quoted source of infomation, maybe all those others were just repeating what he says, as I have above. Hence my "right or wrong" qualifier. With my layout, installed in a building with only 7' ceilings, having the gates right off the main trunk presented no hardship. It may be that putting them there gained me little or nothing, but I figured it wouldn't lose me anything, either.

[JimD]

I am a mechanicl engineer by education but I have not done any work on DC calculations so I don't think my opinions are especially valuable on this topic. I will comment anyway, however.

Bill's website is interesting but I haven't done anything his way yet. He has data to back up his views, I just think the size of DC that he wants us all to have is unrealistic for a home shop - at least it is to me. Tied to the huge DC is the concept of a trunk line of major diameter with smaller drops for the tools. Putting the blast gate next to the trunk line makes sense if you have one but I do not. He is kind of saying put the blast gate close to the DC, however. It is just not practical or necessary to use a blast gate on the trunk line.

I ordered a 35A filter earlier this week based upon advice including Bill Pentz's, however. Better bags made a difference but I still get too much fine dust.

Homemade wooden gates work much better for me than the plastic ones I used at first. I think they have quite a bit less resistance and they do not get clogged with sawdust. I have some close to the DC and some right at the tool. I prefer at the tool for convenience but close to the DC makes me less vulnerable to a flex line getting knocked off the solid line or something like that. Getting good gates may make as much difference as where you locate them.

Jim

[vaking]

I am also mechanical engineer by background but this topic is a domain of HVAC engineer more than mechanical. My not very professional opinion here is that putting blast gate closer to DC reduces the effective volume of the system and simplifies its geometry, so it does reduce loss and improves airflow. However, there are many factors that will have same effect. Replacing your T-connectors with Y-connectors, replacing flexible hose with smooth-walled pipe - all these things will improve the airflow. Most likely the position of the gate is the least significant factor out of all mentioned. So if placing the gate closer to the device will allow you to use less flexible hose - so be it. If placing the gate closer to the device will save you some walking to turn off unnecessary DC branch - that's OK too. No matter what you do - you will never capture all the dust.