brian_p 14 Report post Posted July 17, 2009 I've figured out that I have a bad unloader. My machine currently has a trapped pressure unloader with a blue spring. The stats on the machine are 4gpm 4000psi. I want to switch to a flow sensitive unloader. Should I spend the extra $$ on a Giant unloader that can do 4000psi 4.8gpm, or should I buy the General ZK1 that is only good to 3600psi 10.8gpm and run at a lower pressure? Is there any reason to run 4000psi? This pump is attached to an 18hp briggs through a gear reduction. If the pump ever goes I know I'd be better with a pump that can pump out more gpm, but then the Giant unloader will be a bottleneck. So bottom line, giant or general unloader? Thanks for your unput Share this post Link to post Share on other sites
homer 64 Report post Posted July 18, 2009 Are you sure you have a 4 GPM @ 4000 PSI? If you are using a 13 HP engine it is impossible to have that spec. Although there are quite a few manufacturers advertising 4 @ 4000 with a 13 the best you can achieve is 3500 PSI with that engine. Here is the calculation for Gas engine. GPM (4) X PSI (4000) divided by 1100 = 14.54 HP required. Manufactueres will put a 4000 PSI rated pump on their machine but they don't sell it with a pressure guage for obvious reasons. So - I wouldn't try to size an unloader based on their claims. Now - unloaders. You may also want to conister the VB-10 unloader. Of all the 'soft touch' unloaders this has a great track record. They are much easier to adjust that the typical flow unloaders. Share this post Link to post Share on other sites
brian_p 14 Report post Posted July 18, 2009 The pump is a T9281 General. Specs are 4/4000, 18hp, not 13hp. Gear reduction. The frame is stamped for those specs also... I probably shouldn't be running the pump at rated capacity, I just wonder if 4000psi would ever be necessary? I am intrigued by the compensating unloader, but looks like operating pressure is 3200psi (PDF) It says max is 3600.... Now the ZK1 just has the max pressure of 3600... It would probably be safe to assume the operating pressure should be 3200 also.. Based on what I have, what unloader would you recommend? I already have my shopping cart full on your site as I type this! Share this post Link to post Share on other sites
homer 64 Report post Posted July 18, 2009 I still like the VB10. Don't worry about running the unloader at 3600. Share this post Link to post Share on other sites
