Torque multiplication and pump torque

[mechmos]

Hi,

I am looking into the compatibility of pumps and engines and am struggling to get my head around the torque issue. Two questions really, firstly the transmsission. I am considering the Allison HT700 series and in the handbook it states that the overall torque multiplication is the product of the torque convertor mulitplication and the gear ratio, is this correct? i only ask as in first gear this factor works out at 21.519 which seems very high!
Second question is to do with the triplex pump, I am tryin to determine what the maximum torque the pump is able to withstand. The pump manual doesn't give this figure but it does give a maximum rod load and i have found on an old spreadsheet the equation that states -

Torque=(Rod load*number of cylinders*stroke)/(2*pi*gear ratio*mechanical efficiency)

Can anyone tell me if this is also correct as it doesn't seem to make any sense to me!

I appreciate that this is probably not the right forum but i was hoping someone might be able to shed some light on it for me.

Thanks,

mechmos

 

[NormPeterson]

The torque converter portion of that 21.519 only occurs under certain circumstances. The rest of the time it's less. It would be 1.0 if there is an activated lockup mechanism present.

Can't help with Q#2. Sorry.


Norm

 

[mechmos]

Thanks Norm,

That helps on the first question. It is still high for the HT700 series with a first gear ratio of 7.97 but it makes a lot more sense than 21.519.

Thanks

 

[Fabrico]

My 1985 OEM Allison manual on the 700-D Series shows a converter multipliction ratio of 3.04:1 and a first gear ratio of 7.97 on the 5-speed versions. So it's worse at 24.229!

Is the pump PTO driven or direct? Hard to imagine having an engine and automatic transmission doing whatever they want in front of a direct drive pump. Their job is to keep that shaft turning no matter what.

 

[dicer]

21.519 is high???? Did you mean LOW??? As the direction through the transmission makes this a "REDUCTION" so it is a LOW GEAR ratio. And if you really meant it is too high, then you would need to add an auxiliary transmission behind it or find one with a greater reduction gear set.

And the max Torque for converter reduction is only at stalled transmission input shaft or turbine. That ratio tapers off as turbine speed increases. Thats the nice thing about a torque converter it is similar to a CVT in starting out conditions.
I don't understand the pump question, is this to be attached to the transmission? And with a pump who cares how much torque it will take? If it is to be used as something like a hydraulic pump, you will have a relief valve to dump any excess pressure. Just go by the manufactures directions for installation.

 

[mechmos]

Thanks for the responses, yes I did mean too low for 21.519.
I should maybe have explained the application, it is for oilfield use and yes we just directly couple the triplex pump to the transmission via a driveshaft. The pump is capable of pumping water to 20,000PSI.

Dicer I am intrigued as to why you think you can't have too much torque into a pump, or care whether you put too much in. Surely putting too much into the pump would cause some sort of damage?

Thanks,

mechmos

 

[dicer]

Well, first of all with that application why would you want to use a torque converter? You could use a mechanical clutch and still use an automatic transmission for ratio changes if needed.
And as far as the not caring about the torque into the pump here are some examples of small pumps on large torquey engines. Take for instance an old D7, D8, D9 Cat dozer, there are at least two pumps driving off the accessory section directly coupled. One is for the hydraulic system and the other is for the transmission.
Neither one of those pumps is designed to take the full 270 to 300 hp at around 1200 to 1300 rpms and the associated torque, but they are both driven by the engine.
Why don't they incure this damage that you are concerned about? Its very simple, a pressure regulating system, ie a valve that dumps excess oil back to the sump or reservoir when before maximum is reached, the manufacture will spec the maximums that you are concerned about. If not then you can always calculate the safe loads the pump shaft will live best at, using a pressure regulating system to set the load where you need it. So who is the manufacture and are there any specs for the pump?
The specs are usually give in Gallons per minute, and operating pressure. Some pumps can have a regulating bypass system. So what is the pump going to pump? Is there a valve to unload the pump as it is started or does it start under load?

 

[BrianPetersen]

Is this a pump for a hydraulic system? (cylinders, hydraulic motors and the like?)

If that's the case, I don't get why you don't use a plain ordinary pressure-compensated variable-displacement hydraulic pump and directly couple it to the engine, no transmission needed. It will be way more efficient that way, and you can organize the controls for the pump displacement to get various relationships between output pressure and volume.

Most industrial hydraulic power-packs work like this. Most of them are driven by an electric motor, but that doesn't make any difference.

 

[mechmos]

Thanks for all the responses, you have been a great help. I think that this forum was porobably the wrong one for the pump question as you possibly don't quite understand the application of the pump I am using. Thanks for trying to help though.

mechmos

 

[Fabrico]

Assuming the pump is direct coupled with no pressure relief, it would not be difficult to limit torque by either the engine throttle or transmission gear selection. FWIW, that transmission's governor and throttle detent are also easily accessible.

 

[dicer]

You haven't told us the application so all we can do is GUESS what you want.
Need specifics and the application. What is it gona pump and how much is it gona pump, and what pressure does it need?