Episode: 2452
Title: HPR2452: Hydraulic Heavy Scale Project
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr2452/hpr2452.mp3
Transcribed: 2025-10-19 03:18:15

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This is HPR Episode 2452 entitled Hydraulic Heavy Scale Project.
It is hosted by David Whitman and in about 22 minutes long and Karima Clean Flag.
The summary is Hydraulic Black Mod DIY Travel Trailer Balance.
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Hello, to you out there in Hacker Public Radio Land.
My name is David Whitman.
I'm from Oregon.
Today I want to describe a project that I did to build a scale for weighing a trailer tongue
for a heavy trailer that I have.
And I was curious as to what the actual weight was.
My hitches rated it on my truck at 1,400 pounds.
And the trailer is quite large.
So you want to balance the load on that.
Technically you should haul or trailers mostly are designed
so that 10% of the load should be on the hitch.
The rest on the tires.
I could buy a scale which is a hydraulic piston with a pressure gauge on it online
for $135 or pay even more than that for it at the trailer supply house.
But instead I took a hydraulic jack and added a pressure gauge to it
so that I could read the internal pressure of the hydraulic oil
and therefore compute the weight of the trailer tongue.
A hydraulic jack which is typically called a bottle jack does look like a bottle.
It has an outside case on the outside of it.
It looks like the bottle.
It will have a base.
The base will have a needle valve to let oil from the internal cylinder
that will move the piston back into the reservoir body or the bottle.
And it will also have a small piston that you pump that forces oil in underneath the piston
that actually does the lifting on the jack.
So if you force a liquid into a confined space,
it will not compress and it will start applying pressure to the closed vessel.
And so something will have to give.
In this case the jack is designed with a piston in covering up the confined space.
And as the oil is forced in there is a seal.
And since it's the weak spot, the piston will rise and pick up the load that is above it.
Using oil is good. You could use water I suppose.
But using oil is good because it lubricates everything.
And it also seems pretty stable.
So the...
You can use...
Let me tell you any type of oil in this jack.
You could use engine oil if you wanted to.
I will use transmission oil or power steering fluid or jack fluid,
whatever I have or tractor hydraulic fluid.
It really doesn't really make a whole lot of difference.
If you look at the outside of the jack,
there will be a rubber plug on the outside that you'll see.
And that is actually where the oil goes in that.
And it's kind of funny because if you turn the jack over,
it will not spill the oil,
but it actually,
because it's a rubber plug and it's at the atmospheric side of the reservoir,
it will let the air in and out.
And it's very slow and you don't notice it, but it also seals when the jack is just turned over.
So my goal is to attach a pressure gauge to the jack
in such a way that it measures the internal pressure that's inside the piston
or that picks the piston up that's inside the cylinder that the jack piston goes into.
Now, like I said, oil is incompressible.
So the oil,
if you continually force some oil into a closed vessel like this jack
and it goes over pressure,
something is going to give.
And in this case, probably the seal,
if it was too heavy of a load to seal,
would probably leak past and it wouldn't lift the load up.
So, but supposing you had a way to produce pressure and to push pressure
into say a closed vessel like,
let's say a can or a bottle or something,
if you continually do that,
you have enough,
you get enough pressure and there's something will burst and give.
Now, we're going to be lifting heavy weights with this jack
and so much heavier than you can handle by hand.
You would never be able to hold this trailer tongue with your arms.
And so think of what you could hold in your hand easily and have control of
and that would be something like an apple, an orange or a baseball.
And once you get heavier than that,
you have to think about what you're doing and how you're controlling that.
And I'm saying this as a safety warning because once you lift a trailer tongue
or something that's heavy with a jack,
you want to be sure that if something goes wrong,
that you know which way it'll go so that you can stay out of the way.
And this is really important for your safety because a lot of people have been injured
or killed from heavy weights that they didn't know what they were doing
or lost control of them.
Now, you will see online some people will talk about making a scale
also that can hold a heavy weight between a hook and the weight.
And they'll pick it up with a crane or a come along or some sort of a winch and suspended.
And these devices can be very, once you get a load suspended,
sometimes you can't tell where they're going to go.
So just be careful when you're handling something that's heavy.
You know, think about what consequences of what's going to happen.
You can watch some YouTube movies about people loading heavy equipment
and crane fails where the crane lets go of the load or tips the crane over
and you can get an idea of what the physics are for lifting something.
So just be careful, chalk the wheels on the trailer,
make sure that you have everything in place.
So to build my scale, I simply took and I had a drill bit
and I bore into the side of the jack in order to get an oil passage to the outside,
put a 90 degree fitting on that in a pressure gauge.
In my case, I picked a pressure gauge that was 10,000 pounds per square inch
where it looks like it's 700 bar.
And we don't use bar so much here.
A lot of people that use hydraulics here won't understand bar.
But, and it also says it's 100 times kilopest scales.
So there's, I guess, three scales on here.
I use the outside one, pounds per square inch,
because we measure things in pounds in the United States.
Now, in order to make this work, I'm going to have to know the internal size of the piston that is in the jack.
That takes taking it apart.
When you first look at these, they do not look like they can be taken apart,
but they simply can.
You put the base in a vice.
There is usually a nut of some sort on the top,
and you unscrew the nut.
And it'll come off.
The bottle part will pull out of the seal that's at the bottom,
and will leave you with an internal cylinder with a piston in it.
And you want to pull the piston out of the cylinder.
And then remove this cylinder, usually with a,
there'll be threaded in to the bottom.
And you'd want to remove it, maybe, I did on mine.
And I'm not sure that was a good idea, but I did.
But at this point, you'll want to measure and record somewhere.
So don't forget it.
What the diameter or the actual inside of that piston is.
Or the, yeah, the piston, the cylinder, actually,
because the piston will be smaller,
but it'll have a seal on it to make it work.
At the top, when you take the big nut off,
there'll be a gland up there.
Also, on the outside of the jack, there is a rubber plug,
and that is where the oil goes in to the bottle.
Once you get it apart, you'll see this.
It's pretty simple, but it lets it vent,
and you can fill more oil in there if you want to,
and you will be putting oil into it later.
When you take this apart, there's going to be some mass.
So do it with something underneath it to collect the oil.
And I would throw that oil away.
Somewhere on the base, you will want to drill a small hole.
It can be very small in the beginning.
And drill into the underneath where the piston is in the reservoir area.
You just have to look at that, choose a place.
Usually the bases are made of cast iron.
You want to stay away from the jacked piston sight of this.
And where the needle valve is, let the pressure back out.
And so measuring it is the first thing,
then drilling the pilot hole in to let the oil out.
Now, metal shavings get into things, and they'll cut rubber seals.
So you want to clean that out really well.
You chose not to take the piston out.
You'll have a little harder time cleaning it,
but the piston will remain sealed, which probably is a good idea.
The piston I'm talking about, the cylinder will remain sealed.
Now, at the top of the cylinder,
there's going to be a real small hole.
And when the jack is raised up and gets near the top,
there will be a very small hole.
You can look for it and find it.
You can leave the oil so it'll let it go back.
So it'll only go so high.
And once it tries to go higher, the oil relieves back,
and it'll settle back again, and won't fall any further
if everything is working okay.
Now, I will mention here that the jacking oil
that is put into the jack underneath the piston
and into the cylinder, there's a needle valve
that will equalize in the bottle area or the reservoir area
and the bottle to the inside of the cylinder.
And the needle valve has to be closed to raise the jack
and then you open it to let the jack down.
The piston is smaller in size,
and it doesn't really matter how much smaller.
The smaller it is, the easier it is going to be to work
and force a small amount of oil in under the piston,
and the piston then will raise.
But in order to hold the oil from rushing back
into where the piston is,
because it has to be supplied by the reservoir as a check valve,
I don't mess with any of that stuff.
Don't take any of that apart if you can help it.
It just doesn't work out really.
And I will say here that I have a jack here
that was built in 2000.
Again, see the, I believe 2009, a Willemar,
8,000 pound jack.
And the one, if you buy one today,
they'll look almost identical.
And the sizes of the parts will be almost identical.
So you'll want to drill a hole in at the bottom,
go through the cast iron,
and you'll have to pierce clear into the reservoir area
and not get any of the other porting
that is in there to relieve the pressure and that.
And then you'll want to clean that up really well.
You want to get all the metal shavings and filings out.
You can use water to do this.
You can wash all the parts in water.
You can dry it then with a hairdryer or a heat gun.
Or, you know, it's probably the best way to blow it off with air.
Let it drip dry to get,
it won't really rest that much.
You're going to be putting oil right back into it.
So once your pilot hole is drilled into the inside,
I use like an eighth inch bit.
It doesn't have to be very big.
But on the outside, you'll want to have a 90 degree fitting
to put your hydraulic gauge on.
And for that, you'll have to drill another hole
that will fit a tap that will put threads on that in that hole.
So you can make it a little bit bigger.
And I would drill a very small pilot hole
and then a larger hole that's the right size to collect the tap
and thread that in.
You could use a starter tap to begin with.
That's shaped more pointed.
It'll start to hole a little straighter.
And you just run these in by hand.
You don't have one look it up online.
Check it out and try to borrow one from a friend if you don't own it.
And then you, as soon as it's done, you get the tapping.
You've got to clean it up after you've done all the metal work.
You get the tap put in there and you get your fitting.
In my case, I used a quarter inch fitting pipe fitting.
And it goes out a 90 degree to a quarter inch female.
It's a male quarter inch to a female thread on the other end of the 90.
And that points the gauge up.
And you have to kind of do a little finagling.
When you do it, you'll see you have to put the gauge on while it's down
and then rotate it up.
You could just put the gauge on the other way.
And it would be fine.
But I bought a 10,000 pound gauge from Amazon 10 to 20 dollars.
They're not that much.
The fitting is probably three or four dollars.
And I got a 10,000 pound gauge.
I also bought a 2,000 pound gauge because I figured that it would be a little more accurate
if I was closer to what I wanted to measure.
Or maybe it was a 3,000 pound gauge.
But they're not that expensive.
You would want to get a liquid fill gauge that is a board on tube gauge.
You would want to get a liquid filled one if you can.
In fact, I wouldn't, I would use a liquid filled one.
They have dampening in them, used to measure hydraulic pressure.
Now as soon as it's, you get it all tapped out and everything.
You can get your fitting set up.
Put the bottle back on, put the nut back on the top, refit down.
Like I said, need a vice and a large adjustable wrench.
Or a end wrench.
Or a pipe wrench to do this work.
And once that's done, you're all back together.
Set your gauge, rotate it around so that it's standing up.
And then pull the rubber plug out.
Or unless you have it, you might have taken it out already.
It's a good idea to take it out while the bottle, the reservoir bottle is off.
And then lay the, put the jack up right and then get some oil back into it up to the level
with the piston flare down up to the level of the plug.
Or maybe just a little shy of that.
If you get it clipped to the top to shake a little out, maybe it's a good idea.
So that it doesn't get right up there because it will weep out a little bit if it's under pressure at that point.
And so there you have it.
You would put your jack underneath the load you want to measure.
Close the needle valve, pump it up and read off the gauge.
And then you would simply do some mathematics based on the diameter
or the radius of the piston.
And I believe it's two times, I believe it's the radius squared times pi.
Give you the surface area.
And if you multiply the pounds or the pressure in the jack, whatever you use,
I use pounds per square inch by the actual square inches of the cylinder.
The cylinder should give you a reading that's accurate or that's pretty accurate to measure your load.
And I use this, my brother had the other kind, the $135 kind.
And I double checked against what he had.
And my jack actually at one PSI will put out or at one PSI will lift one pound.
In other words, if I got to 2,000 PSI, I could be pretty confident I had 2,000 pounds on it.
Now, at this point, since I now know and I found out my trailer was quite a bit too heavy in the front, it was about 2,100 pounds.
So then I had to do something to make it lighten up in the front.
And for that, I measured the distance from the hitch point, tip of the hitch, back to the wheels.
And this trailer actually has two axles on it, so I measured to the center point, the fulcrum point,
but I'd call that the fulcrum point, right between the center of the two wheels and then measure the total distance of the trailer.
So then I just make a ratio out of that, and I cannot remember what it was.
And that would tell me how much weight I needed to load into the back of the trailer by that ratio in order to then balance the trailer out to get the right weight on the safe weight on the hitch.
And in my case, my trailer is actually called a toy hauler.
You can put an ATV, which we actually own one, but it's not really for going up and tearing up the country.
My wife uses for dog training to put her gear out and stuff to train these retriever dogs,
which I don't think anyone in Hacker Public Radio would be interested in retriever dog training or anything.
So I guess we won't be doing a show about that, but I don't carry the ATV with me, but we carry dog kennels and stuff.
So I actually then built a rack that went on a rear of the trailer.
There's a big back door that opens up where you can drive the ATV, and you're actually supposed to carry one in there to make it balance out correctly,
but I put a rear rack on it and move the dog kennels and stuff to the outside, and also put two 15 gallon jugs of water on there to add some extra weight.
And it's always nice to have fresh water. We do what they call boondock camping, where we go out somewhere.
We have a power generator, and we will in battery power, and we'll set up out in a field somewhere.
I don't actually train the dogs, she does, and I go along to do work, I guess.
And so they're boondocking, and it's nice to have a little fresh water with you, so I always carry a little Milton.
It's not Milton Greek, it's a knulty water with me from St. Helens.
So I balanced out my trailer that way, I feel pretty confident and safe.
You know, with the load that I'm carrying, I can take this jack scale with me.
I have one little problem with it, is it somehow, for some reason, drifts down a bit.
Drift down quite a bit, you pump it up, and it will drift right back down.
But at the maximum pressure that you get if you read that, that is the weight of it, and I'm not sure why it's doing that.
And I only have fragments of time to do things it seems like, so this is working fine for its intended purpose, but I can't really use it as a jack.
I guess I could pull the pressure gauge off and plug that and see if the leaking is in the actual pressure gauge somehow, but I really don't see how they could be.
It's probably something to do with when I unthreaded the piston, and that's why I probably wouldn't unthread the piston on the next one, and I may try another one.
These things, these eight ton jacks, or four ton, I guess four ton jacks.
These four ton jacks come, you can buy them for $10 when they come on sale, so they're not very expensive.
And they're nice to have around, I have a group of them around.
And I like to, you know, they're nice for like lifting, I'm working on an old 57, 1957 GMC truck.
And so I have it up on a rack so I can put, you know, four jacks underneath it and lift it up, and then it's nice to be able to take all the wheels off and whatever.
So when they come on sale, I buy extra one, so I may play around with that a little bit more.
I was trying to think if there's anything else I wanted to share about this, it really works out good.
Oh, there is another method for doing folkroom base weighing.
You can take a beam and put underneath your trailer tongue, and then block it up, measuring out a known distance on, say, the right hand side,
and a longer distance on the left hand side, put a block under that and put it on a bathroom scale.
And you can do the ratio thing, you can look that up online too.
It's nice to be able to know how much something weighs.
There is all the time for people towing things around the United States that they don't have a knowledge of how the trailer, what, how, what weight it is.
And it will actually ride better when you have the correct amount of weight, toe better, and it's a lot safer.
Thank you very much for listening.
I hope this was interesting to leave somebody, and I've tried to get a birthday episode out for the last, this would be the third year, and it's still at least the time I'm recording this 2017.
So this is, I'm sharing my birthday cake with you today, and I would encourage you to get the recorder out of your phone, and let's do it, your own topic, your own project, your own episode for Hacker Public Radio.
Thank you very much.
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