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Anonymous Poster

Hydraulic Press vs Bolt Torque

05/23/2010 8:04 AM

I want to assemble a plate type heat exchanger temporarily. It is designed to be assembled with 12 1-1/4" NC bolts torqued at 400 ft-lbs.

I understand that what I want to do is unconventional, but I want to assemble the exchanger bundle with 4 hydraulic jacks rather than the bolts.

Can someone give me a ballpark tonnage figure for the jacks I would require? I'd also be interested (more interested actually) in the thinking behind any answers.

Thanks in advance.

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#1

Re: Hydraulic Press vs Bolt Torque

05/23/2010 2:48 PM

If there is any leakage in a hydraulic jack, the exchanger plates may separate and leak. Moreover, with fewer jacks than bolts, the end plates of the exchanger may bow outward between the jacks. This plan is inadvisable. If either fluid is dangerous, injury or property damage could result.

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Anonymous Poster
#2
In reply to #1

Re: Hydraulic Press vs Bolt Torque

05/23/2010 4:17 PM

All your advice and observations are appreciated. This is strictly a testing scenario. The setup is a water to glycol exchanger, although in this configuration, both sides would be filled strictly with water.

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#3
In reply to #2

Re: Hydraulic Press vs Bolt Torque

05/23/2010 4:43 PM

This probably wouldn't fly as a permanent arrangement, but it could serve a testing purpose. For one thing, if the actual pressures will be less than what the exchanger is rated for, the earlier concerns might not apply. Multiply the test pressure by the plate area to get the total force; ensure that the total force of the four jacks is greater than that by a suitable factor (such as maybe 2?) For example, if the exchanger is rated at 150 psi, and you put only 30 psi to it, that would seem okay. But by the time you rig up something for the outer ends of the jacks to press against, wouldn't it be just as easy to use the bolts without fully torquing them down? If the bolts are extra long to accommodate future expansion, you could buy or make a nut runner to speed up this process.

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#4

Re: Hydraulic Press vs Bolt Torque

05/23/2010 10:26 PM

what is the pressure on the head? What are the square inches of the head?

Multiply and you get the force needed to just keep the pressure in. The add a 2 x safety factor.

In any event, jacks seep fluid and would have to be kept pressurized with a pump to maintain the pressure.

It seems you want some sort of quuick change rig for testing repeatedly in a short time.

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#5

Re: Hydraulic Press vs Bolt Torque

05/23/2010 10:52 PM

The distance from bolt-to-bolt centerlines is definite and calculated to be the max. to prevent leakage, therefore no way to increase that distance between bolts even you increase the dia. of bolt, except in certain limits. Also, no way to use 10 bolts instead of 12 of the same dia.

If you need to use jacks rather than the bolts, I think you need 12 jacks not 4.

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#6

Re: Hydraulic Press vs Bolt Torque

05/23/2010 11:25 PM

Try balancing jack force by 2:1 yokes, six spanning adjacent 'bolt' stubs, then three each pushing on the centres of two adjacent yokes. Three hydraulic jacks, dimensioned as in previous posts, will provide the force. Balls (or rollers) in sloppy retainers, may be used at the contact points. See whipple tree!

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#7

Re: Hydraulic Press vs Bolt Torque

05/23/2010 11:34 PM

What our posters tell you here is a good advise. To calculate your pressure for your cylinders, you might need this formula:

T = (C x D x P x A) / (no of screws)

T = torque per screw (Nm)

C = torque coefficient; generalized values for copper/mild steel (0.36 dry, 0.18 lubricated)

D = nominal screw size (m)

P = desired pressure (force per unit area) (N/sq m)

A = surface area (sq mm)

As you see some parameters are "variables" . I do not guarantee the accuracy for your purpose. If you try to accomplish it anyhow, you should stiffen out the plates to make them suitable for 4 pressure points. Find also your value for C. And move the elements around to calculate P. You'll be surprised.

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#8

Re: Hydraulic Press vs Bolt Torque

05/24/2010 7:13 AM

i used to work of plate and frames and my men still due. I am used to seeing a plate pack thickness on the label, not a bolt torque rating. We use our own rig to pull the pack to thickness and then we tighten the bolts. Our rig employs a 20 ton 'porto-power' so we don't have much to begin with and it is definitely not using the full capacity, but we have to move it to get the pack evenly compressed. If you are within the minimum spec's you could have a small leak but not a major blow-out so i would go for it. If you leak, just put one or two bolts near the leak and pull the pack in with no water pressure in the pack and it's resolved. We have tried several mechanical devices to speed up the bolt tightening process and they all failed quickly.

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#9

Re: Hydraulic Press vs Bolt Torque

05/24/2010 7:41 AM

A DANGEROUS idea.

PHE's are designed to withstand pressure/high temps, please look at the design of PHE's and note the number of bolts that are installed to pull together the rather THICK back plates to compress the plates and seals. These bolts are to distribute the compression EQUALLY over the area of the plates and compress equally the seal in-between each plate.

Any change to the design will end up with fluid leaks at high pressure.

I cannot understand WHY you want to change the design..... with this type of equipment you cannot do anything "TEMPORARILY".

YOU WILL KILL SOME ONE.

Do yourself a favour, put it together the way it's been designed

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#10

Re: Hydraulic Press vs Bolt Torque

05/24/2010 11:07 AM

Excellent Idea.

This isn't unconventional at all . In fact, this is a well-known procedure for compressing the plates of a P&F exchanger.

The benefits of this method is that you achieve consistent plate loading since all four tensioners ("jacks") are pressurized simultaneously using a single pump. This can only be done by torquing if four torque wrenches are available. In addition to much more accurate loads compared to torquing, tensioning is much quicker.

To determine an equivalent tensioner operating pressure, you'd first have to know how tight the bolts have to be. This is not your 400 ft-lb torque figure! Torque is only a measurement of the resistance to input force. Since it's unlikely that you have this value, the best thing to do is to torque the four tie bars to 400 ft-lbs and measure the stack distance. Then, release the loads, apply the tensioners and pressurize until the same dimension is achieved.

* I just want to make clear that the tensioners are not affixed permanently to the tie rods; The existing nuts are used. After the plates are compressed, the nuts are run down. At that point, the tensioner pressure is released and the tools are removed. Disassembly is in reverse.

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#11
In reply to #10

Re: Hydraulic Press vs Bolt Torque

05/24/2010 11:56 AM

bolt integrity I have to tip my hat, fantastic solution to a long standing problem

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#14
In reply to #10

Re: Hydraulic Press vs Bolt Torque

05/26/2010 3:04 PM

Thanks for all the replies. Great information that will help me immensely.

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#12

Re: Hydraulic Press vs Bolt Torque

05/24/2010 11:13 PM

It looks as though the end plate on that HX spans about 8 feet between the upper and lower bolts. The internal pressures must not be very high.

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#13
In reply to #12

Re: Hydraulic Press vs Bolt Torque

05/25/2010 7:56 AM

Nor are they high in any gasketed P&F Heat Exchanger.

The tensioning technology used in these applications is identical to that used in very high pressure S&T Heat Exchangers. Here's a link explaining how it works in either case:

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