Anyone Know How to Fix a Mole?

[Rusty Bolt]

Does anyone out there know about moles, AKA missiles AKA pneumatic boring tools?

I rented a 4 inch mole to put a chase under my driveway. It's a Vermeer VPT400 if that matters. I also rented a towable air compressor to drive it.

It don't work so good.

It just sits there and hammers, oscillating back and forth a few inches each time. If anything it seems to want to back away from the side of the trench. It's had hours to do its job. Prying with a digging bar to encourage it to go forward didn't help but it did give me a good workout.

The rental company sent a mechanic out - twice. He took the tool apart, cleaned it, and checked the length of the internal tube. He has a lot of experience with pneumatic tools. He was on the phone with Vermeer's customer support and they weren't any help.

The rental company is shipping a new tool in. The new tool has been tested, so it should work which will solve my problem but ...

My question is why doesn't it work? Nobody seems to know much about them. It's a pretty simple tool inside. You screw the air inlet (and internal tube) in to make it hammer harder in the forward direction. Screw the inlet out to put it in reverse.

 

[Milton Shaw]

When I have seen them used they had to push on it to get it started into the ground, once it was in around a foot or so it would take off. .

 

[Rusty Bolt]

OK, I finally figured it out. Three days to figure out the tool and 12 minutes to punch the hole. I'll document the fix here for posterity.

Just as I was about to give up, I called the manufacturer's tech support one last time. They had been worthless so far but the alternatives for poking a hole under my driveway were unappealing. The guy I got this time was mostly worthless but he gave me a clue. He asked the question: What air pressure was I running? I told him the compressor was set at 125 PSI. The Vermeer sales literature says the tool takes 110 PSI. The support guy said that sometimes they ran them at 90 PSI.

The rental company mechanic, my dirt guy, and I had all tried throttling the air pressure to the mole and it hadn't changed its behavior. 125 PSI is less than 15% more than 110 PSI, so it didn't seem like likely fix but I decided to try one more time.

Then I noticed that the tail piece unscrews rapidly when run at 125 PSI; several seconds to go from forward to neutral and reverse. You can't really tell that the tools is turning when watching the tool jump around because it's a pretty featureless piece of pipe.

This time I did two things at the same time: I turned the tailpiece all the way in and I used the ball valve on the oilier to ramp up the pressure slowly until it just started to hammer. Then I used a little pressure on the hose to get it to hit the side of the trench. After a few seconds, the mole took off like a scared jackrabbit (well maybe a frightened snail) and started digging.

12 minutes later, I had my 24 foot long hole.

I'm happy with the rental company, Sunbelt Rentals. They tried very hard to make this work. They shipped a tool from another location (which I agreed to pay for), they sent out a mechanic, they overnight shipped a second tool (partially to make up with a screwup between them and the trucking company), and they delivered the new tool to me right after they got the replacement tool.

Today I returned Sunbelt's mole and compressor and showed them how to make the mole work. They gave me a no-charge rental so I'm not out any money except diesel for the air compressor.

Vermeer was a real disappointment. Someone should have known and documented that their moles are so sensitive to air pressure. There should be engraved markings on the case about forward and reverse. If moles are so sensitive to air pressure, they ought to put a pressure regulator on the oilier or at least engrave a warning on the tool body.

 

[RPH]

Sorry to hear Vermeer was disappointing. My experience has been the total opposite with them. I have an old trencher with backhoe. I called to purchase the manuals for the beast, they asked for serial numbers and I supplied. Got all four manuals for the beast for free.
Glad that you got that twelve minutes of hard work done though and in the end that’s all that matters.

 

[ant.foste]

I had never heard of such a thing until this thread. Very cool! While it was a mostly frustrating experience, I'm glad you shared it. I learned something new today and am completing reasons for needing one.

 

[vavet]

Dang it...gj strikes again. I didn’t know this tool existed. What do you think happens now?

 

[bczygan]

What is the diameter of the hole it digs?

How deep is it?

What are you running through it? Will it be sleeved? What kind of pipe?

Sunbelt has some good stuff.

Bill

 

[Rusty Bolt]

@RPH Well at least Vermeer Customer Support was there and answered the phone.

@ant.foste

That Vemeer video is a good video that you found. I see they throttled the air both at the compressor and at the oilier without explanation. A subtlety that's very easy to miss. Clearly those guys knew they needed to do throttle the air. It's too bad the info isn't shared in the manual, a FAQ, or passed on to customer support. Or maybe even a pressure gauge with a green band for the right air pressure. Nah, that would add $5 manufacturing cost to a $3K tool.

That pulling carrot is pretty slick too. Putting something like PEX or plastic conduit through the hole can be a PITA because they aren't straight and tend to dig into the side of the hole. When I ran my 1.25 inch MDPE gas line under the driveway through some 2 inch EMT, I taped a 2 foot piece of closet rod in the end to keep it from digging into the sides.

@bczy.gan

The first mole that I got has a 4 inch diameter. It's a little hard for an old guy like me to handle at 135 lbs. (40 years ago, no problem) The second tool was a 3 inch diameter. The 3 inch tool made a hole that was a little too small for 2.5 inch PVC conduit. 2 inch PVC conduit was an easy fit. Vermeer sells Hole Hammers from 2 inches to 5.25 inches. I don't know about other brands.

Here's a Vermeer sales sheet https://www.vermeer.com/documents/2/1420/Hole_Hammer_Positive_Turn_Reverse_Sales_Sheet_LR.pdf

My hole turned out to be about 24' long. The video linked by ant.foste above says holes up to 70 feet.

I put the hole about 30 inches below my driveway and sleeved it with PVC conduit. I didn't need to sleeve it but after going through the trouble of poking the hole under the driveway, sleeving the hole means there is a little bit of future proofing. I ran a one inch PEX line through it that is acting like a flexible conduit for a data line out to my shop. The PEX line comes up inside the utility room of my new shop.

I learned about moles by watching the Comcast guys install some conduit under my driveway. They tried to avoid having to dig through tree roots on the other side by going shallow and angling up. They also hit the last course of pavers on my driveway.

Some videos of similar tools show a nice launch platform. It's basically a platform with a piece of angle iron that acts like a cradle to support the tool with a post that sticks up out of the trench. At the top of the post is a sight that you use to aim the mole.

I just used a piece of string to line the mole. I had to adjust the aim after it got a foot or so into the hole. I just used a digging bar to pry the mole over a few inches to get it lined up. The mole came out within about 4 inches of where I was aiming.

If I need to put another hole under my driveway, I'll definitely try to rent another mole. It's not cheap; ~$200/day for the compressor and $370/day for a 4 inch mole plus I had originally agreed to another $120 to ship the mole to the local Sunbelt store. The thought of tearing up my paver driveway and then patching it, is not appealing but that's what most contractors around here do. Looking at the local boring company's web site, I don't think they'll get out of bed, let alone put down their coffee for $1K.

A year and a half ago, I needed to put a gas line under my driveway. Nobody local had a mole to rent. One rental company said "we used to have one but we never rented it, so we sent it to Sacramento". So, I used 2 inch EMT and a sledgehammer. It took me about a week.

I think moles are a great solution to a fairly common problem. I don't know why they aren't more popular. Maybe a manufacturer, like Vermeer, should through some money at This Old House or Bob Villa to get them to use one on a project?

 

[homebuilt burner]

I have used a BorZit. It runs with a 3/4” drill and a garden hose.