How to increase "flow" on a splitter???

[AKKAMAAN]

Reading threads and posts about flow, power, force, pressure, restriction, rpm, displacement etc etc.

There is a misunderstanding among many posters, about how increased restriction decrease flow, or how less restriction increase flow......

I will here try to explain how it works!!

We start with the pressure side of the pump!

First of all we need to agree about the type of pump we are using.

We are using a fixed displacement pump. Pump displacement is the theoretical volume per revolution of fluid, that the pump can "push" forward. (This volume per revolution, can only be changed in a variable displacement pump). Common unit for pump displacement is CUbicInch, CUI, or CubicCentiMeter, ccm or just cc.

Flow is the volume of fluid that the pump "pushes forward" over a certain time. Common unit is GallonPerMinute, GPM, or LiterPerMinute, l/min.

Pump flow will overcome restriction in the system by an increase of pressure. One can say that restriction increases pressure. When pressure increases, the internal leaks increases too. For the efficiancy of the splitter cylinder, the internal leakage in the pump itself and the Control Valve, CV, are the main losses of flow. Hydraulic pumps are rated between 85-95% volumetric efficiancy at a certain maximum pump pressure.
This also means that a pump is more volume efficient at low pressure than high pressure. Fluid viscosity is another important factor on the efficiancy. Thicker fluid decreases internal leakage, but increases pressure from restriction. It is important to have the right viscosity. Viscosity changes with fluid temperture. So the right operating temperature is also important. 104-140F or 40-60C.

Here is what happens when we are increasing size on fittings, ports and hoses!

• the decreased pressure will decrease the internal leakage

• the decreased pressure will decrease the load on the engine, and we might get a slightly higher rpm on the pump

If we are using a two stage pump, we know that the pump switches to high pressure/low flow at about 650PSI....

• If we are lucky, the increased size on fittings, ports and hoses, might lower the pressure that much so pump will stay in low pressure/high flow stage.

These three bullets/points are the only flow benefits we get from increasing size on fittings, ports and hoses. And we can not expect more than a few % increase of flow, by increasing size on fittings, ports and hoses.

Overall benefits from increasing size on fittings, ports and hoses, is that the decreased pressure, will make it easier for motor/engine to turn the pump, and it will take less power (gas). We will also get less problems with high temperture in entire system.

The condition for this discussion above, is that we have a fully closed center of the CV, so the whole flow can be directed to the cylinder. Also that the Relief Valve is not bypassing any flow. in other words, there can not be any other bypasses, than natural internal leakage.

----------

The suction side is very different, because the pump will have to "pull" the fluid from the tank. It is actually the air pressure in the tank that pushes the fluid to the pump. Everbody knows that air pressure is limited to about 15psi, and below that it is complete Vacuum! Gravity (head) is the only other force that can help pusshing the fluid into the pump. This makes the flow into pump very dependent on low restriction and high push pressure from air AND gravity combined.
If we restrict suction side of pump, fluid will start vapor and cavitate. These bubbles of vapor will be part of a decreased flow through the pump. The cavitaion will literally, eat up the pump over some time.
Suction side benefits from having pump installed below the tank, or at least below the fluid level in the tank. (positive head)

In my opinion, it is more important to make sure suction side have a minimum of restriction, before we start working on improving the pressure side.
One of the things to concider first is the presense of a suction filter/strainer, which is a very controversial and discussed issue.

----------

Conclusion:

Overall, the pump will not increase flow, just "like that", if we increase size on fittings, ports and hoses. Other "good things" have to happen first.
We can still not expect more than a few % increase of flow, by increasing size on fittings, ports and hoses. But we can expect lower pressure, better power efficiancy and better temperture control.

To really increase flow(cycle speed) on a splitter cylinder, it will take higher rpm's and/or a larger pump displacement.

 

[Fronty Owner]

You didn't touch on relief valves.
typically, inline with your pressure line, if your restriction is running your pressure near the relief valve pressure, your loosing flow and generating heat there also. Then again, the higher pressure your operating at is putting more heat in your oil too.
What Im trying to say is, larger lines will at the very least put less heat in your oil.

 

[AKKAMAAN]

You didn't touch on relief valves.
typically, inline with your pressure line, if your restriction is running your pressure near the relief valve pressure, your loosing flow and generating heat there also. Then again, the higher pressure your operating at is putting more heat in your oil too.
What Im trying to say is, larger lines will at the very least put less heat in your oil.

Thank you for your reply Fronty Owner!
You obviously did not read my entire post....that is exactly what I posted...

I quote my self here...

The condition for this discussion above, is that we have a fully closed center of the CV, so the whole flow can be directed to the cylinder. Also that the Relief Valve is not bypassing any flow. in other words, there can not be any other bypasses, than natural internal leakage.

We will also get less problems with high temperture in entire system.

opcorn:

 

[mga]

good post, man, i wondered about that.

 

[AKKAMAAN]

good post, man, i wondered about that.

 

[Woodchip1]

Pumps are designed to have leaks also known as slippage and there is no getting around that. So the increased resistance will have an effect on the volume of the pump. At least according to Mr. Mobley.

 

[avalancher]

Pump flow will overcome restriction in the system by an increase of pressure

Only to a certain degree!Here are two cases that prove my point.

I rebuilt a Cat,dont remember the model number now,it was some time ago.Bearings where burnt, camshaft wiped,and a considerable amount of damage done.After the rebuild I tested the oil pump to acertain that I had not only proper volume but proper pressure.Pump was down by 15lbs no matter where I measured around the block.A new pump did the same thing.then I noticed that new oil lines had been replaced recently and discovered that they had been made at a local hydralic shop.Fittings where smaller than the original hoses.Replaced and pressure went right back to factory specs on a new engine.Restriction will increase pressure but decrease volume.When fluid passes through a restriction then resumes its path in its normal sized cavity pressure drops right back down to its previous state,unless of coarse a load is applied.

And a more simple approach,when I purchased my home, the original builder plumbed the line from the well to the house with one inch lines.Upon entering the home it switched to 1/2 where it went to the manifold.Water pressure and volume was poor at all faucets until I found the problem and replaced the line with a one inch piece.Water volume went from 3 gallons per minute to almost 8 at our bathtub, and the water pressure maintained a constant 65psi instead of dropping down to 40psi after you opened the faucet.Here again, the smaller line provided the restriction,resulting in a low volume.

 

[AKKAMAAN]

Only to a certain degree!Here are two cases that prove my point.

And a more simple approach,when I purchased my home, the original builder plumbed the line from the well to the house with one inch lines.Upon entering the home it switched to 1/2 where it went to the manifold.Water pressure and volume was poor at all faucets until I found the problem and replaced the line with a one inch piece.Water volume went from 3 gallons per minute to almost 8 at our bathtub, and the water pressure maintained a constant 65psi instead of dropping down to 40psi after you opened the faucet.Here again, the smaller line provided the restriction,resulting in a low volume.

thx for your reply...I will be back later...but your house water supply does not play the same game...centrifugal pump , not a displacement pump....

also think about where the lost oil went on that cat..

 

[Woodchip1]

The pressure in the home changed due to an open system. Pressure remains the same through out the system only if the fluid can not escape.

 

[triptester]

A fixed displacement pump's flow is not really fixed that is why they are less than 100% efficient. As pressure increases efficiency decreases as does flow, when restrictions are encountered.
I you take two 5 gallon buckets filled with water , one with a 3/4" hose at the bottom and the other with a 1/2" hose. Which will drain faster? The one with the 3/4" hose. In order for the bucket with the 1/2" hose to empty at the same rate you have to add pressure.

In a typical log splitter when small hoses are used pressure will build faster causing the bypass to open sooner with a 2-stage pump reducing flow and slowing the movement of the cylinder.

 

[mga]

so...why wouldn't they make hydraulic systems with the largest hoses and fittings possible?

there has to be some formula used when making hydraulic parts like cylinders, pumps, control valves, etc. they can't just be left up to what each of the manufacturers feels it should be.

for example, why not put 1" ports on a 3 inch diameter cylinder?

 

[Woodchip1]

Pumps have a rated gpm output at a given rpm. What ever size hose will allow this flow is all you need. Smaller will restrict it and bigger is just a waste.

 

[AKKAMAAN]

oK...Back now.....last reply from my cellph....

I think some of you guys are mixing up different systems here.....

First, there are diffeent types of pumps....
In a hydrostatic system, like a logsplitter, excavator, power steering etc....we use a POSITIVE DISPLACEMENT PUMP. These pump are designed to move "all" fluid forward, as long as pump shaft is turning.

In a water supply system in a house, we use centrifugal pump.

The differens between those two is that the positive displacement pump forces the fluid forward. Such a pump need a Relif Valve, RV, to set maximum system pressure. Pump will keep moving fluid forward, even when RV is open at max set pressure.

A centrigugal pump do not need a RV, the pump itself bypasses the fluid backwards to suction side when outlet line is blocked (faucet closed). The system pressure is more or less proportional to the pump rpm.

Another way the define the differens between these two pumps, is that you can pour fluid from inlet straight thru to the outlet of the centrifugal pump. That is not possible on a positive displacement pump.

The positive displacement pump have some "slippage" or internal leakage, wich also fills a purpose for lubrication. As I mentioned in my first posting, internal leakage increases with pressure.

Hydro static hydraulics concider fluid to be CONTAINED, and can as contained be in two different states.....NO FLOW or with FLOW (FLOW is fluid moving)

As I pointed out in my first post, in a hydrostatic system, you can not increase flow, with larger hoses, fittings etc, unless changing pump rpm's or the displacement. But I also gave that statement a condition.....
-NO BY PASSES OF FLUID
I also said that we can gain some flow from larger hoses and fittings, but very marginal....because if we for example upsize from 3/8 to 1/2", because we are only reducing the pressure drop "marginally"...

Let us say a gear pump have 90% efficiancy at 3000psi and 100% efficiancy at "0" psi. That tells us that we get 1% per 300psi we can reduce pressure...
I dont think we can expect more than a few 2% gain of flow by upsizing hoses and fittings. BUT we can save us some energy and over heating problems.

 

[AKKAMAAN]

Pumps are designed to have leaks also known as slippage and there is no getting around that. So the increased resistance will have an effect on the volume of the pump. At least according to Mr. Mobley.

So I said in my post too!!

Pump flow will overcome restriction in the system by an increase of pressure. One can say that restriction increases pressure. When pressure increases, the internal leaks increases too. For the efficiancy of the splitter cylinder, the internal leakage in the pump itself and the Control Valve, CV, are the main losses of flow. Hydraulic pumps are rated between 85-95% volumetric efficiancy at a certain maximum pump pressure.
This also means that a pump is more volume efficient at low pressure than high pressure. Fluid viscosity is another important factor on the efficiancy. Thicker fluid decreases internal leakage, but increases pressure from restriction. It is important to have the right viscosity. Viscosity changes with fluid temperture. So the right operating temperature is also important. 104-140F or 40-60C.

 

[AKKAMAAN]

Only to a certain degree!Here are two cases that prove my point.

Restriction will increase pressure but decrease volume.

Volume?? or Flow??

Good you mentioned VOLUME because oil compresses a little when pressureized, so we get a lower volume of oil when pressure increases...about 1% for 3000psi, depending on oils bulk modulus...

Volume=FLOW....flow out from pump only decreases the same amount the internal lekage in pump increases....very marginally...see my other post....

 

[Blazin]

Good info! Now someome throw this dude a cookie already!

 

[Woodchip1]

Here is one for you to figure out. A week or two ago a guy on here was having a problem with a home built splitter having very slow cycle times. He tried everything and couldn't figure out why. Someone suggested that even though he had adaquite sized lines he might want to check the fittings to make sure none were of the restricter type with the smaller ID. He found he infact did have one that had a smaller ID. He changed it and just like magic his problem was solved.

 

[AKKAMAAN]

A fixed displacement pump's flow is not really fixed that is why they are less than 100% efficient.As pressure increases efficiency decreases as does flow, when restrictions are encountered.

Thats true! But I pointed that out in my post too!!

I you take two 5 gallon buckets filled with water , one with a 3/4" hose at the bottom and the other with a 1/2" hose. Which will drain faster? The one with the 3/4" hose. In order for the bucket with the 1/2" hose to empty at the same rate you have to add pressure.

That is true too, BUT it don't apply in this case, because it is not a hydrostatic system, fluid not contained. That is like mixing apples and oranges...

In a typical log splitter when small hoses are used pressure will build faster causing the bypass to open sooner with a 2-stage pump reducing flow and slowing the movement of the cylinder.

That is true too! And I never said anything else......

 

[AKKAMAAN]

so...why wouldn't they make hydraulic systems with the largest hoses and fittings possible?

Because larger fittings and hoses cost more each and per foot. Also larger hoses will need more wiring to hold the same pressure as a smaller size....It is all about money...and manufacturers cut these corners all the time....both on logsplitters and "excavators"....These savings for them is STRAIGHT PROFIT, and the equipment owner has to take the beat, with over heating and inefficiancy.....flow will stay about the same though....

Here is a picture that explains this...Same discussion but about the sizing of a cylinder mantle...

there has to be some formula used when making hydraulic parts like cylinders, pumps, control valves, etc. they can't just be left up to what each of the manufacturers feels it should be.

for example, why not put 1" ports on a 3 inch diameter cylinder?

Such a big port would take a lot more metal structure around it to make the pressure rating....if you double the port diameter, you will cut the pressure rating in "half"....

 

[AKKAMAAN]

Here is one for you to figure out. A week or two ago a guy on here was having a problem with a home built splitter having very slow cycle times. He tried everything and couldn't figure out why. Someone suggested that even though he had adaquite sized lines he might want to check the fittings to make sure none were of the restricter type with the smaller ID. He found he infact did have one that had a smaller ID. He changed it and just like magic his problem was solved.

Yes...great post!!
that fitting restricted the line so pressure increased!!!! So far so good!!

BUT, he was using a two stage pump, which shifts to "low gear' at about 650psi....so when he change to a normal fitting, the pressure went below 650psi and pump kicked in the high gear....problem solved.....I also pointed this option out in my first post....

• If we are lucky, the increased size on fittings, ports and hoses, might lower the pressure that much so pump will stay in low pressure/high flow stage.